Add JSON Patch functions and immutability helpers

.mocharc.json

@@ -1,3 +0,0 @@
-{
-  "test": "./src/**/*.test.js"
-}

package-lock.json

@@ -139,9 +139,9 @@
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@@ -172,12 +172,6 @@
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@@ -264,12 +244,6 @@
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@@ -286,6 +260,45 @@
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       }
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+        "wrap-ansi": "^5.1.0"
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+          "dev": true,
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@@ -418,6 +437,15 @@
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       }
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+      "dev": true,
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@@ -425,14 +453,6 @@
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@@ -553,6 +567,12 @@
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@@ -760,18 +800,18 @@
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-      "version": "7.1.1",
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@@ -787,7 +827,7 @@
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         "minimatch": "3.0.4",
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+      "resolved": "https://registry.npmjs.org/ms/-/ms-2.1.1.tgz",
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+    },
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       "resolved": "https://registry.npmjs.org/node-environment-flags/-/node-environment-flags-1.0.6.tgz",
@@ -1004,14 +910,6 @@
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-          "resolved": "https://registry.npmjs.org/semver/-/semver-5.7.1.tgz",
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-          "dev": true
-        }
       }
     },
     "normalize-path": {
@@ -1078,12 +976,27 @@
         "p-try": "^2.0.0"
       }
     },
+    "p-locate": {
+      "version": "3.0.0",
+      "resolved": "https://registry.npmjs.org/p-locate/-/p-locate-3.0.0.tgz",
+      "integrity": "sha512-x+12w/To+4GFfgJhBEpiDcLozRJGegY+Ei7/z0tSLkMmxGZNybVMSfWj9aJn8Z5Fc7dBUNJOOVgPv2H7IwulSQ==",
+      "dev": true,
+      "requires": {
+        "p-limit": "^2.0.0"
+      }
+    },
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       "version": "2.2.0",
       "resolved": "https://registry.npmjs.org/p-try/-/p-try-2.2.0.tgz",
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       "dev": true
     },
+    "path-exists": {
+      "version": "3.0.0",
+      "resolved": "https://registry.npmjs.org/path-exists/-/path-exists-3.0.0.tgz",
+      "integrity": "sha1-zg6+ql94yxiSXqfYENe1mwEP1RU=",
+      "dev": true
+    },
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       "version": "1.0.1",
       "resolved": "https://registry.npmjs.org/path-is-absolute/-/path-is-absolute-1.0.1.tgz",
@@ -1096,12 +1009,6 @@
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       "dev": true
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-    "pathval": {
-      "version": "1.1.0",
-      "resolved": "https://registry.npmjs.org/pathval/-/pathval-1.1.0.tgz",
-      "integrity": "sha1-uULm1L3mUwBe9rcTYd74cn0GReA=",
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@@ -1221,6 +1128,12 @@
         "chokidar": ">=2.0.0 <4.0.0"
       }
     },
+    "semver": {
+      "version": "5.7.1",
+      "resolved": "https://registry.npmjs.org/semver/-/semver-5.7.1.tgz",
+      "integrity": "sha512-sauaDf/PZdVgrLTNYHRtpXa1iRiKcaebiKQ1BJdpQlWH2lCvexQdX55snPFyK7QzpudqbCI0qXFfOasHdyNDGQ==",
+      "dev": true
+    },
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       "version": "2.1.2",
       "resolved": "https://registry.npmjs.org/serialize-javascript/-/serialize-javascript-2.1.2.tgz",
@@ -1286,6 +1199,16 @@
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       "dev": true
     },
+    "string-width": {
+      "version": "2.1.1",
+      "resolved": "https://registry.npmjs.org/string-width/-/string-width-2.1.1.tgz",
+      "integrity": "sha512-nOqH59deCq9SRHlxq1Aw85Jnt4w6KvLKqWVik6oA9ZklXLNIOlqg4F2yrT1MVaTjAqvVwdfeZ7w7aCvJD7ugkw==",
+      "dev": true,
+      "requires": {
+        "is-fullwidth-code-point": "^2.0.0",
+        "strip-ansi": "^4.0.0"
+      }
+    },
     "string.prototype.trimend": {
       "version": "1.0.1",
       "resolved": "https://registry.npmjs.org/string.prototype.trimend/-/string.prototype.trimend-1.0.1.tgz",
@@ -1328,6 +1251,15 @@
         "es-abstract": "^1.17.5"
       }
     },
+    "strip-ansi": {
+      "version": "4.0.0",
+      "resolved": "https://registry.npmjs.org/strip-ansi/-/strip-ansi-4.0.0.tgz",
+      "integrity": "sha1-qEeQIusaw2iocTibY1JixQXuNo8=",
+      "dev": true,
+      "requires": {
+        "ansi-regex": "^3.0.0"
+      }
+    },
     "strip-indent": {
       "version": "3.0.0",
       "resolved": "https://registry.npmjs.org/strip-indent/-/strip-indent-3.0.0.tgz",
@@ -1403,11 +1335,14 @@
         "is-number": "^7.0.0"
       }
     },
-    "type-detect": {
+    "which": {
-      "version": "4.0.8",
+      "version": "1.3.1",
-      "resolved": "https://registry.npmjs.org/type-detect/-/type-detect-4.0.8.tgz",
+      "resolved": "https://registry.npmjs.org/which/-/which-1.3.1.tgz",
-      "integrity": "sha512-0fr/mIH1dlO+x7TlcMy+bIDqKPsw/70tVyeHW787goQjhmqaZe10uwLujubK9q9Lg6Fiho1KUKDYz0Z7k7g5/g==",
+      "integrity": "sha512-HxJdYWq1MTIQbJ3nw0cqssHoTNU267KlrDuGZ1WYlxDStUtKUhOaJmh112/TZmHxxUfuJqPXSOm7tDyas0OSIQ==",
-      "dev": true
+      "dev": true,
+      "requires": {
+        "isexe": "^2.0.0"
+      }
     },
     "which-module": {
       "version": "2.0.0",
@@ -1422,37 +1357,43 @@
       "dev": true,
       "requires": {
         "string-width": "^1.0.2 || 2"
+      }
+    },
+    "wrap-ansi": {
+      "version": "5.1.0",
+      "resolved": "https://registry.npmjs.org/wrap-ansi/-/wrap-ansi-5.1.0.tgz",
+      "integrity": "sha512-QC1/iN/2/RPVJ5jYK8BGttj5z83LmSKmvbvrXPNCLZSEb32KKVDJDl/MOt2N01qU2H/FkzEa9PKto1BqDjtd7Q==",
+      "dev": true,
+      "requires": {
+        "ansi-styles": "^3.2.0",
+        "string-width": "^3.0.0",
+        "strip-ansi": "^5.0.0"
       },
       "dependencies": {
         "ansi-regex": {
-          "version": "3.0.0",
+          "version": "4.1.0",
-          "resolved": "https://registry.npmjs.org/ansi-regex/-/ansi-regex-3.0.0.tgz",
+          "resolved": "https://registry.npmjs.org/ansi-regex/-/ansi-regex-4.1.0.tgz",
-          "integrity": "sha1-7QMXwyIGT3lGbAKWa922Bas32Zg=",
+          "integrity": "sha512-1apePfXM1UOSqw0o9IiFAovVz9M5S1Dg+4TrDwfMewQ6p/rmMueb7tWZjQ1rx4Loy1ArBggoqGpfqqdI4rondg==",
-          "dev": true
-        },
-        "is-fullwidth-code-point": {
-          "version": "2.0.0",
-          "resolved": "https://registry.npmjs.org/is-fullwidth-code-point/-/is-fullwidth-code-point-2.0.0.tgz",
-          "integrity": "sha1-o7MKXE8ZkYMWeqq5O+764937ZU8=",
           "dev": true
         },
         "string-width": {
-          "version": "2.1.1",
+          "version": "3.1.0",
-          "resolved": "https://registry.npmjs.org/string-width/-/string-width-2.1.1.tgz",
+          "resolved": "https://registry.npmjs.org/string-width/-/string-width-3.1.0.tgz",
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+          "integrity": "sha512-vafcv6KjVZKSgz06oM/H6GDBrAtz8vdhQakGjFIvNrHA6y3HCF1CInLy+QLq8dTJPQ1b+KDUqDFctkdRW44e1w==",
           "dev": true,
           "requires": {
+            "emoji-regex": "^7.0.1",
             "is-fullwidth-code-point": "^2.0.0",
-            "strip-ansi": "^4.0.0"
+            "strip-ansi": "^5.1.0"
           }
         },
         "strip-ansi": {
-          "version": "4.0.0",
+          "version": "5.2.0",
-          "resolved": "https://registry.npmjs.org/strip-ansi/-/strip-ansi-4.0.0.tgz",
+          "resolved": "https://registry.npmjs.org/strip-ansi/-/strip-ansi-5.2.0.tgz",
-          "integrity": "sha1-qEeQIusaw2iocTibY1JixQXuNo8=",
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           "dev": true,
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-            "ansi-regex": "^3.0.0"
+            "ansi-regex": "^4.1.0"
           }
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       }
@@ -1478,72 +1419,28 @@
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       "dev": true
     },
-    "yargs-unparser": {
+    "yargs": {
-      "version": "1.6.0",
+      "version": "13.3.2",
-      "resolved": "https://registry.npmjs.org/yargs-unparser/-/yargs-unparser-1.6.0.tgz",
+      "resolved": "https://registry.npmjs.org/yargs/-/yargs-13.3.2.tgz",
-      "integrity": "sha512-W9tKgmSn0DpSatfri0nx52Joq5hVXgeLiqR/5G0sZNDoLZFOr/xjBUDcShCOGNsBnEMNo1KAMBkTej1Hm62HTw==",
+      "integrity": "sha512-AX3Zw5iPruN5ie6xGRIDgqkT+ZhnRlZMLMHAs8tg7nRruy2Nb+i5o9bwghAogtM08q1dpr2LVoS8KSTMYpWXUw==",
       "dev": true,
       "requires": {
-        "flat": "^4.1.0",
+        "cliui": "^5.0.0",
-        "lodash": "^4.17.15",
+        "find-up": "^3.0.0",
-        "yargs": "^13.3.0"
+        "get-caller-file": "^2.0.1",
+        "require-directory": "^2.1.1",
+        "require-main-filename": "^2.0.0",
+        "set-blocking": "^2.0.0",
+        "string-width": "^3.0.0",
+        "which-module": "^2.0.0",
+        "y18n": "^4.0.0",
+        "yargs-parser": "^13.1.2"
       },
       "dependencies": {
-        "cliui": {
+        "ansi-regex": {
-          "version": "5.0.0",
+          "version": "4.1.0",
-          "resolved": "https://registry.npmjs.org/cliui/-/cliui-5.0.0.tgz",
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-          "dev": true
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-        "find-up": {
-          "version": "3.0.0",
-          "resolved": "https://registry.npmjs.org/find-up/-/find-up-3.0.0.tgz",
-          "integrity": "sha512-1yD6RmLI1XBfxugvORwlck6f75tYL+iR0jqwsOrOxMZyGYqUuDhJ0l4AXdO1iX/FTs9cBAMEk1gWSEx1kSbylg==",
-          "dev": true,
-          "requires": {
-            "locate-path": "^3.0.0"
-          }
-        },
-        "is-fullwidth-code-point": {
-          "version": "2.0.0",
-          "resolved": "https://registry.npmjs.org/is-fullwidth-code-point/-/is-fullwidth-code-point-2.0.0.tgz",
-          "integrity": "sha1-o7MKXE8ZkYMWeqq5O+764937ZU8=",
-          "dev": true
-        },
-        "locate-path": {
-          "version": "3.0.0",
-          "resolved": "https://registry.npmjs.org/locate-path/-/locate-path-3.0.0.tgz",
-          "integrity": "sha512-7AO748wWnIhNqAuaty2ZWHkQHRSNfPVIsPIfwEOWO22AmaoVrWavlOcMR5nzTLNYvp36X220/maaRsrec1G65A==",
-          "dev": true,
-          "requires": {
-            "p-locate": "^3.0.0",
-            "path-exists": "^3.0.0"
-          }
-        },
-        "p-locate": {
-          "version": "3.0.0",
-          "resolved": "https://registry.npmjs.org/p-locate/-/p-locate-3.0.0.tgz",
-          "integrity": "sha512-x+12w/To+4GFfgJhBEpiDcLozRJGegY+Ei7/z0tSLkMmxGZNybVMSfWj9aJn8Z5Fc7dBUNJOOVgPv2H7IwulSQ==",
-          "dev": true,
-          "requires": {
-            "p-limit": "^2.0.0"
-          }
-        },
-        "path-exists": {
-          "version": "3.0.0",
-          "resolved": "https://registry.npmjs.org/path-exists/-/path-exists-3.0.0.tgz",
-          "integrity": "sha1-zg6+ql94yxiSXqfYENe1mwEP1RU=",
           "dev": true
         },
         "string-width": {
@@ -1565,47 +1462,29 @@
           "requires": {
             "ansi-regex": "^4.1.0"
           }
-        },
-        "wrap-ansi": {
-          "version": "5.1.0",
-          "resolved": "https://registry.npmjs.org/wrap-ansi/-/wrap-ansi-5.1.0.tgz",
-          "integrity": "sha512-QC1/iN/2/RPVJ5jYK8BGttj5z83LmSKmvbvrXPNCLZSEb32KKVDJDl/MOt2N01qU2H/FkzEa9PKto1BqDjtd7Q==",
-          "dev": true,
-          "requires": {
-            "ansi-styles": "^3.2.0",
-            "string-width": "^3.0.0",
-            "strip-ansi": "^5.0.0"
-          }
-        },
-        "yargs": {
-          "version": "13.3.2",
-          "resolved": "https://registry.npmjs.org/yargs/-/yargs-13.3.2.tgz",
-          "integrity": "sha512-AX3Zw5iPruN5ie6xGRIDgqkT+ZhnRlZMLMHAs8tg7nRruy2Nb+i5o9bwghAogtM08q1dpr2LVoS8KSTMYpWXUw==",
-          "dev": true,
-          "requires": {
-            "cliui": "^5.0.0",
-            "find-up": "^3.0.0",
-            "get-caller-file": "^2.0.1",
-            "require-directory": "^2.1.1",
-            "require-main-filename": "^2.0.0",
-            "set-blocking": "^2.0.0",
-            "string-width": "^3.0.0",
-            "which-module": "^2.0.0",
-            "y18n": "^4.0.0",
-            "yargs-parser": "^13.1.2"
-          }
-        },
-        "yargs-parser": {
-          "version": "13.1.2",
-          "resolved": "https://registry.npmjs.org/yargs-parser/-/yargs-parser-13.1.2.tgz",
-          "integrity": "sha512-3lbsNRf/j+A4QuSZfDRA7HRSfWrzO0YjqTJd5kjAq37Zep1CEgaYmrH9Q3GwPiB9cHyd1Y1UwggGhJGoxipbzg==",
-          "dev": true,
-          "requires": {
-            "camelcase": "^5.0.0",
-            "decamelize": "^1.2.0"
-          }
         }
       }
+    },
+    "yargs-parser": {
+      "version": "13.1.2",
+      "resolved": "https://registry.npmjs.org/yargs-parser/-/yargs-parser-13.1.2.tgz",
+      "integrity": "sha512-3lbsNRf/j+A4QuSZfDRA7HRSfWrzO0YjqTJd5kjAq37Zep1CEgaYmrH9Q3GwPiB9cHyd1Y1UwggGhJGoxipbzg==",
+      "dev": true,
+      "requires": {
+        "camelcase": "^5.0.0",
+        "decamelize": "^1.2.0"
+      }
+    },
+    "yargs-unparser": {
+      "version": "1.6.0",
+      "resolved": "https://registry.npmjs.org/yargs-unparser/-/yargs-unparser-1.6.0.tgz",
+      "integrity": "sha512-W9tKgmSn0DpSatfri0nx52Joq5hVXgeLiqR/5G0sZNDoLZFOr/xjBUDcShCOGNsBnEMNo1KAMBkTej1Hm62HTw==",
+      "dev": true,
+      "requires": {
+        "flat": "^4.1.0",
+        "lodash": "^4.17.15",
+        "yargs": "^13.3.0"
+      }
     }
   }
 }

package.json

@@ -11,12 +11,13 @@
   "dependencies": {
     "@fortawesome/free-regular-svg-icons": "5.13.0",
     "@fortawesome/free-solid-svg-icons": "5.13.0",
+    "lodash": "4.17.15",
     "svelte-awesome": "2.3.0"
   },
   "devDependencies": {
     "@rollup/plugin-commonjs": "11.1.0",
     "@rollup/plugin-node-resolve": "7.1.3",
-    "mocha": "7.1.1",
+    "mocha": "7.1.2",
     "rollup": "2.7.2",
     "rollup-plugin-livereload": "1.2.0",
     "rollup-plugin-svelte": "5.2.1",

src/App.svelte

@@ -2,7 +2,7 @@
 	import Icon from 'svelte-awesome'
 	import { faSearch  } from '@fortawesome/free-solid-svg-icons'
 	import Node from './JSONNode.svelte'
-	import { search } from './utils'
+	import { search } from './search'
 	import { beforeUpdate, afterUpdate } from 'svelte'
 
 	export let searchText = ''

src/JSONNode.svelte

@@ -1,5 +1,6 @@
 <script>
-  import { getType, SEARCH_PROPERTY, SEARCH_VALUE } from './utils'
+  import { SEARCH_PROPERTY, SEARCH_VALUE } from './search'
+  import { getJSONNodeType } from './utils/typeUtils.js'
 
   export let key = 'root'
   export let value
@@ -12,7 +13,7 @@
 
   let limit = DEFAULT_LIMIT
 
-  $: type = getType(value)
+  $: type = getJSONNodeType(value)
 
   $: props = type === 'object'
     ? Object.keys(value).map(key => {

src/search.js

@@ -1,14 +1,8 @@
+import { getJSONNodeType } from './utils/typeUtils'
+
 export const SEARCH_PROPERTY = Symbol('searchProperty')
 export const SEARCH_VALUE = Symbol('searchValue')
 
-export function getType (json) {
-  return Array.isArray(json)
-    ? 'array'
-    : json && typeof json === 'object'
-      ? 'object'
-      : 'value'
-}
-
 export function search (key, value, searchText) {
   let results
 
@@ -16,7 +10,7 @@ export function search (key, value, searchText) {
     results = createOrAdd(results, SEARCH_PROPERTY, true)
   }
 
-  const type = getType(value)
+  const type = getJSONNodeType(value)
   if (type === 'array') {
     value.forEach((item, index) => {
       let childResults = search(index, item, searchText)

src/types.js

@@ -0,0 +1,58 @@
+/** JSDoc type definitions */
+
+/**
+ * @typedef {{} | [] | string | number | boolean | null} JSON
+ */
+
+/**
+ * @typedef {{
+ *   name: string?,
+ *   mode: 'code' | 'form' | 'text' | 'tree' | 'view'?,
+ *   modes: string[]?,
+ *   history: boolean?,
+ *   indentation: number | string?,
+ *   onChange: function (patch: JSONPatchDocument, revert: JSONPatchDocument)?,
+ *   onChangeText: function ()?,
+ *   onChangeMode: function (mode: string, prevMode: string)?,
+ *   onError:  function (err: Error)?,
+ *   isPropertyEditable: function (Path)?
+ *   isValueEditable: function (Path)?,
+ *   escapeUnicode: boolean?,
+ *   expand: function(path: Path) : boolean?,
+ *   ajv: Object?,
+ *   ace: Object?
+ * }} Options
+ */
+
+/**
+ * @typedef {string[]} Path
+ */
+
+/**
+ * @typedef {{
+ *   op: 'add' | 'remove' | 'replace' | 'copy' | 'move' | 'test',
+ *   path: string,
+ *   from?: string,
+ *   value?: *
+ * }} JSONPatchOperation
+ */
+
+/**
+ * @typedef {JSONPatchOperation[]} JSONPatchDocument
+ */
+
+/**
+ * @typedef {{
+ *   fromJSON: function(json: JSON, previousObject: * | undefined),
+ *   toJSON: function(object: *),
+ *   clone: function(object: *)
+ * }} JSONPatchOptions
+ */
+
+/**
+ * @typedef {{
+ *   patch: JSONPatchDocument,
+ *   revert: JSONPatchDocument,
+ *   error: Error | null
+ * }} JSONPatchResult
+ */

src/utils.test.js

@@ -1,13 +0,0 @@
-import { getType } from './utils.js'
-import assert from 'assert'
-
-describe('utils', () => {
-  it('should test equality of positive values', function () {
-    assert.strictEqual(getType([]), 'array')
-    assert.strictEqual(getType({}), 'object')
-    assert.strictEqual(getType(null), 'value')
-    assert.strictEqual(getType(2), 'value')
-    assert.strictEqual(getType('hello'), 'value')
-    assert.strictEqual(getType('hello'), 'value')
-  })
-})

src/utils/immutabilityHelpers.js

@@ -0,0 +1,293 @@
+import { isObjectOrArray } from  './typeUtils.js'
+
+/**
+ * Immutability helpers
+ *
+ * inspiration:
+ *
+ * https://www.npmjs.com/package/seamless-immutable
+ * https://www.npmjs.com/package/ih
+ * https://www.npmjs.com/package/mutatis
+ * https://github.com/mariocasciaro/object-path-immutable
+ */
+
+/**
+ * Shallow clone of an Object, Array, or value
+ * Also copies any symbols on the Objects and Arrays
+ * @param {*} value
+ * @return {*}
+ */
+export function shallowCloneWithSymbols (value) {
+  if (Array.isArray(value)) {
+    // copy array items
+    let arr = value.slice()
+
+    // copy all symbols
+    Object.getOwnPropertySymbols(value).forEach(symbol => arr[symbol] = value[symbol])
+
+    return arr
+  }
+  else if (typeof value === 'object') {
+    // copy properties
+    let obj = {}
+    for (let prop in value) {
+      if (value.hasOwnProperty(prop)) {
+        obj[prop] = value[prop]
+      }
+    }
+
+    // copy all symbols
+    Object.getOwnPropertySymbols(value).forEach(symbol => obj[symbol] = value[symbol])
+
+    return obj
+  }
+  else {
+    return value
+  }
+}
+
+/**
+ * helper function to get a nested property in an object or array
+ *
+ * @param {Object | Array} object
+ * @param {Path} path
+ * @return {* | undefined} Returns the field when found, or undefined when the
+ *                         path doesn't exist
+ */
+export function getIn (object, path) {
+  let value = object
+  let i = 0
+
+  while(i < path.length) {
+    if (isObjectOrArray(value)) {
+      value = value[path[i]]
+    }
+    else {
+      value = undefined
+    }
+
+    i++
+  }
+
+  return value
+}
+
+/**
+ * helper function to replace a nested property in an object with a new value
+ * without mutating the object itself.
+ *
+ * @param {Object | Array} object
+ * @param {Path} path
+ * @param {*} value
+ * @return {Object | Array} Returns a new, updated object or array
+ */
+export function setIn (object, path, value) {
+  if (path.length === 0) {
+    return value
+  }
+
+  if (!isObjectOrArray(object)) {
+    throw new Error('Path does not exist')
+  }
+
+  const key = path[0]
+  const updatedValue = setIn(object[key], path.slice(1), value)
+  if (object[key] === updatedValue) {
+    // return original object unchanged when the new value is identical to the old one
+    return object
+  }
+  else {
+    const updatedObject = shallowCloneWithSymbols(object)
+    updatedObject[key] = updatedValue
+    return updatedObject
+  }
+}
+
+/**
+ * helper function to replace a nested property in an object with a new value
+ * without mutating the object itself.
+ *
+ * @param {Object | Array} object
+ * @param {Path} path
+ * @param {function} callback
+ * @return {Object | Array} Returns a new, updated object or array
+ */
+export function updateIn (object, path, callback) {
+  if (path.length === 0) {
+    return callback(object)
+  }
+
+  if (!isObjectOrArray(object)) {
+    throw new Error('Path doesn\'t exist')
+  }
+
+  const key = path[0]
+  const updatedValue = updateIn(object[key], path.slice(1), callback)
+  // TODO: create a function applyProp(...) which does the following if/else construct
+  if (object[key] === updatedValue) {
+    // return original object unchanged when the new value is identical to the old one
+    return object
+  }
+  else {
+    const updatedObject = shallowCloneWithSymbols(object)
+    updatedObject[key] = updatedValue
+    return updatedObject
+  }
+}
+
+/**
+ * helper function to delete a nested property in an object
+ * without mutating the object itself.
+ *
+ * @param {Object | Array} object
+ * @param {Path} path
+ * @return {Object | Array} Returns a new, updated object or array
+ */
+export function deleteIn (object, path) {
+  if (path.length === 0) {
+    return object
+  }
+
+  if (!isObjectOrArray(object)) {
+    return object
+  }
+
+  if (path.length === 1) {
+    const key = path[0]
+    if (!(key in object)) {
+      // key doesn't exist. return object unchanged
+      return object
+    }
+    else {
+      const updatedObject = shallowCloneWithSymbols(object)
+
+      if (Array.isArray(updatedObject) && typeof key !== 'symbol') {
+        updatedObject.splice(key, 1)
+      }
+      else {
+        delete updatedObject[key]
+      }
+
+      return updatedObject
+    }
+  }
+
+  const key = path[0]
+  const updatedValue = deleteIn(object[key], path.slice(1))
+  if (object[key] === updatedValue) {
+    // object is unchanged
+    return object
+  }
+  else {
+    const updatedObject = shallowCloneWithSymbols(object)
+    updatedObject[key] = updatedValue
+    return updatedObject
+  }
+}
+
+/**
+ * Insert a new item in an array at a specific index.
+ * Example usage:
+ *
+ *     insertAt({arr: [1,2,3]}, ['arr', '2'], 'inserted')  // [1,2,'inserted',3]
+ *
+ * @param {Object | Array} object
+ * @param {Path} path
+ * @param {*} value
+ * @return {Array}
+ */
+export function insertAt (object, path, value) {
+  const parentPath = path.slice(0, path.length - 1)
+  const index = path[path.length - 1]
+
+  return updateIn(object, parentPath, (items) => {
+    if (!Array.isArray(items)) {
+      throw new TypeError('Array expected at path ' + JSON.stringify(parentPath))
+    }
+
+    const updatedItems = shallowCloneWithSymbols(items)
+    updatedItems.splice(index, 0, value)
+
+    return updatedItems
+  })
+}
+
+/**
+ * Transform a JSON object, traverse over the whole object,
+ * and allow replacing Objects/Arrays/values.
+ * Does not iterate over symbols.
+ * @param {JSON} json
+ * @param {function (json: JSON, path: Path) : JSON} callback
+ * @param {Path} [path]
+ * @return {JSON}
+ */
+export function transform (json, callback, path = []) {
+  const updated1 = callback(json, path)
+
+  if (Array.isArray(json)) { // array
+    let updated2 = undefined
+
+    for (let i = 0; i < updated1.length; i++) {
+      const before = updated1[i]
+      // we stringify the index here, so the Path only contains strings and can be safely
+      // stringified/parsed to JSONPointer without loosing information.
+      // We do not want to rely on path keys being numeric/string.
+      const after = transform(before, callback, path.concat(i + ''))
+      if (after !== before) {
+        if (!updated2) {
+          updated2 = shallowCloneWithSymbols(updated1)
+        }
+        updated2[i] = after
+      }
+    }
+
+    return updated2 ? updated2 : updated1
+  }
+  else if (json && typeof json === 'object') { // object
+    let updated2 = undefined
+
+    for (let key in updated1) {
+      if (updated1.hasOwnProperty(key)) {
+        const before = updated1[key]
+        const after = transform(before, callback, path.concat(key))
+        if (after !== before) {
+          if (!updated2) {
+            updated2 = shallowCloneWithSymbols(updated1)
+          }
+          updated2[key] = after
+        }
+      }
+    }
+
+    return updated2 ? updated2 : updated1
+  }
+  else { // number, string, boolean, null
+    return updated1
+  }
+}
+
+/**
+ * Test whether a path exists in a JSON object
+ * @param {JSON} json
+ * @param {Path} path
+ * @return {boolean} Returns true if the path exists, else returns false
+ * @private
+ */
+export function existsIn (json, path) {
+  if (json === undefined) {
+    return false
+  }
+
+  if (path.length === 0) {
+    return true
+  }
+
+  if (Array.isArray(json)) {
+    // index of an array
+    return existsIn(json[parseInt(path[0], 10)], path.slice(1))
+  }
+  else { // Object
+    // object property. find the index of this property
+    return existsIn(json[path[0]], path.slice(1))
+  }
+}

src/utils/immutabilityHelpers.test.js

@@ -0,0 +1,323 @@
+import { deleteIn, existsIn, getIn, insertAt, setIn, transform, updateIn } from './immutabilityHelpers.js'
+import { expect } from './testUtils.js' // FIXME: replace jest with mocha tests, or move to jest
+
+const test = it // FIXME: replace jest with mocha tests, or move to jest
+
+test('getIn', () => {
+  const obj = {
+    a: {
+      b: {
+        c: 2
+      }
+    },
+    d: 3,
+    e: [
+      4,
+      {
+        f: 5,
+        g: 6
+      }
+    ]
+  }
+
+  expect(getIn(obj, ['a', 'b'])).toEqual({c: 2})
+  expect(getIn(obj, ['e', '1', 'f'])).toEqual(5)
+  expect(getIn(obj, ['e', '999', 'f'])).toBeUndefined()
+  expect(getIn(obj, ['non', 'existing', 'path'])).toBeUndefined()
+})
+
+test('setIn basic', () => {
+  const obj = {
+    a: {
+      b: {
+        c: 2
+      }
+    },
+    d: 3
+  }
+
+  const updated = setIn(obj, ['a', 'b', 'c'], 4)
+  expect(updated).toEqual({
+    a: {
+      b: {
+        c: 4
+      }
+    },
+    d: 3
+  })
+
+  // original should be unchanged
+  expect(obj).toEqual({
+    a: {
+      b: {
+        c: 2
+      }
+    },
+    d: 3
+  })
+
+  expect(obj).not.toBe(updated)
+})
+
+test('setIn non existing path', () => {
+  const obj = {}
+
+  expect(() => setIn(obj, ['a', 'b', 'c'], 4)).toThrow(/Path does not exist/)
+})
+
+test('setIn replace value with object should throw an exception', () => {
+  const obj = {
+    a: 42,
+    d: 3
+  }
+
+  expect(()  => setIn(obj, ['a', 'b', 'c'], 4)).toThrow(/Path does not exist/)
+})
+
+test('setIn replace value inside nested array', () => {
+  const obj = {
+    a: [
+      1,
+      2,
+      {
+        b: 3,
+        c: 4
+      }
+    ],
+    d: 5
+  }
+
+  const updated = setIn(obj, ['a', '2', 'c'], 8)
+
+  expect(updated).toEqual({
+    a: [
+      1,
+      2,
+      {
+        b: 3,
+        c: 8
+      }
+    ],
+    d: 5
+  })
+})
+
+test('setIn identical value should return the original object', () => {
+  const obj = {a:1, b:2}
+
+  const updated = setIn(obj, ['b'], 2)
+
+  expect(updated).toBe(obj) // strict equal
+})
+
+test('setIn identical value should return the original object (2)', () => {
+  const obj = {a:1, b: { c: 2}}
+
+  const updated = setIn(obj, ['b', 'c'], 2)
+
+  expect(updated).toBe(obj) // strict equal
+})
+
+test('updateIn', () => {
+  const obj = {
+    a: {
+      b: {
+        c: 2
+      }
+    },
+    d: 3
+  }
+
+  const updated = updateIn(obj, ['a', 'b', 'c'], (value) => value + 100)
+  expect(updated).toEqual({
+    a: {
+      b: {
+        c: 102
+      }
+    },
+    d: 3
+  })
+
+  // original should be unchanged
+  expect(obj).toEqual({
+    a: {
+      b: {
+        c: 2
+      }
+    },
+    d: 3
+  })
+
+  expect(obj).not.toBe(updated)
+})
+
+test('updateIn (2)', () => {
+  const obj = {
+    a: {
+      b: {
+        c: 2
+      }
+    },
+    d: 3
+  }
+
+  const updated = updateIn(obj, ['a', 'b' ], (obj) => [1,2,3])
+  expect(updated).toEqual({
+    a: {
+      b: [1,2,3]
+    },
+    d: 3
+  })
+})
+
+test('updateIn (3)', () => {
+  const obj = {
+    a: {
+      b: {
+        c: 2
+      }
+    },
+    d: 3
+  }
+
+  const updated = updateIn(obj, ['a', 'e' ], (value) => 'foo-' + value)
+  expect(updated).toEqual({
+    a: {
+      b: {
+        c: 2
+      },
+      e: 'foo-undefined'
+    },
+    d: 3
+  })
+})
+
+test('updateIn return identical value should return the original object', () => {
+  const obj = {
+    a: 2,
+    b: 3
+  }
+
+  const updated = updateIn(obj, ['b' ], (value) => 3)
+  expect(updated).toBe(obj)
+})
+
+test('deleteIn', () => {
+  const obj = {
+    a: {
+      b: {
+        c: 2,
+        d: 3
+      }
+    },
+    e: 4
+  }
+
+  const updated = deleteIn(obj, ['a', 'b', 'c'])
+  expect(updated).toEqual({
+    a: {
+      b: {
+        d: 3
+      }
+    },
+    e: 4
+  })
+
+  // original should be unchanged
+  expect(obj).toEqual({
+    a: {
+      b: {
+        c: 2,
+        d: 3
+      }
+    },
+    e: 4
+  })
+
+  expect(obj).not.toBe(updated)
+})
+
+test('deleteIn array', () => {
+  const obj = {
+    a: {
+      b: [1, {c: 2, d: 3} , 4]
+    },
+    e: 5
+  }
+
+  const updated = deleteIn(obj, ['a', 'b', '1', 'c'])
+  expect(updated).toEqual({
+    a: {
+      b: [1, {d: 3} , 4]
+    },
+    e: 5
+  })
+
+  // original should be unchanged
+  expect(obj).toEqual({
+    a: {
+      b: [1, {c: 2, d: 3} , 4]
+    },
+    e: 5
+  })
+
+  expect(obj).not.toBe(updated)
+})
+
+test('deleteIn non existing path', () => {
+  const obj = { a: {}}
+
+  const updated = deleteIn(obj, ['a', 'b'])
+  expect(updated).toBe(obj)
+})
+
+test('insertAt', () => {
+  const obj = { a: [1,2,3]}
+
+  const updated = insertAt(obj, ['a', '2'], 8)
+  expect(updated).toEqual({a: [1,2,8,3]})
+})
+
+test('transform (no change)', () => {
+  const json = {a: [1,2,3], b: {c: 4}}
+  const updated = transform(json, (value, path) => value)
+  expect(updated).toBe(json)
+})
+
+test('transform (change based on value)', () => {
+  const json = {a: [1,2,3], b: {c: 4}}
+
+  const updated = transform(json,
+      (value, path) => value === 2 ? 20 : value)
+  const expected = {a: [1,20,3], b: {c: 4}}
+
+  expect(updated).toEqual(expected)
+  expect(updated.b).toBe(json.b) // should not have replaced b
+})
+
+test('transform (change based on path)', () => {
+  const json = {a: [1,2,3], b: {c: 4}}
+
+  const updated = transform(json,
+      (value, path) => path.join('.') === 'a.1' ? 20 : value)
+  const expected = {a: [1,20,3], b: {c: 4}}
+
+  expect(updated).toEqual(expected)
+  expect(updated.b).toBe(json.b) // should not have replaced b
+})
+
+test('existsIn', () => {
+  const json = {
+    "obj": {
+      "arr": [1,2, {"first":3,"last":4}]
+    },
+    "str": "hello world",
+    "nill": null,
+    "bool": false
+  }
+
+  expect(existsIn(json, ['obj', 'arr', 2, 'first'])).toEqual(true)
+  expect(existsIn(json, ['obj', 'foo'])).toEqual(false)
+  expect(existsIn(json, ['obj', 'foo', 'bar'])).toEqual(false)
+  expect(existsIn(json, [])).toEqual(true)
+})

src/utils/immutableJSONPatch.js

@@ -0,0 +1,314 @@
+import {
+  deleteIn,
+  existsIn,
+  getIn,
+  insertAt,
+  setIn
+} from './immutabilityHelpers.js'
+import { compileJSONPointer, parseJSONPointer } from './jsonPointer.js'
+import initial from 'lodash/initial.js'
+import isEqual from 'lodash/isEqual.js'
+
+const DEFAULT_OPTIONS = {
+  fromJSON: (json, previousObject) => json,
+  toJSON: (object) => object,
+  clone: (object) => object
+}
+
+/**
+ * Apply a patch to a JSON object
+ * The original JSON object will not be changed,
+ * instead, the patch is applied in an immutable way
+ * @param {JSON} json
+ * @param {JSONPatchDocument} operations    Array with JSON patch actions
+ * @param {JSONPatchOptions} [options]
+ * @return {{json: JSON, revert: JSONPatchDocument, error: Error | null}}
+ */
+export function immutableJSONPatch (json, operations, options = DEFAULT_OPTIONS) {
+  let updatedJson = json
+  let revert = []
+
+  for (let i = 0; i < operations.length; i++) {
+    const operation = operations[i]
+    const path = operation.path ? parseJSONPointer(operation.path) : null
+    const from = operation.from ? parseJSONPointer(operation.from) : null
+
+    switch (operation.op) {
+      case 'add': {
+        const result = add(updatedJson, path, operation.value, options)
+        updatedJson = result.json
+        revert = result.revert.concat(revert)
+        break
+      }
+
+      case 'remove': {
+        const result = remove(updatedJson, path, options)
+        updatedJson = result.json
+        revert = result.revert.concat(revert)
+
+        break
+      }
+
+      case 'replace': {
+        const result = replace(updatedJson, path, operation.value, options)
+        updatedJson = result.json
+        revert = result.revert.concat(revert)
+
+        break
+      }
+
+      case 'copy': {
+        if (!operation.from) {
+          return {
+            json: updatedJson,
+            revert: [],
+            error: new Error('Property "from" expected in copy action ' + JSON.stringify(operation))
+          }
+        }
+
+        const result = copy(updatedJson, path, from, options)
+        updatedJson = result.json
+        revert = result.revert.concat(revert)
+
+        break
+      }
+
+      case 'move': {
+        if (!operation.from) {
+          return {
+            json: updatedJson,
+            revert: [],
+            error: new Error('Property "from" expected in move action ' + JSON.stringify(operation))
+          }
+        }
+
+        const result = move(updatedJson, path, from, options)
+        updatedJson = result.json
+        revert = result.revert.concat(revert)
+
+        break
+      }
+
+      case 'test': {
+        // when a test fails, cancel the whole patch and return the error
+        const error = test(updatedJson, path, operation.value, options)
+        if (error) {
+          return { json, revert: [], error}
+        }
+
+        break
+      }
+
+      default: {
+        // unknown patch operation. Cancel the whole patch and return an error
+        return {
+          json,
+          revert: [],
+          error: new Error('Unknown JSONPatch op ' + JSON.stringify(operation.op))
+        }
+      }
+    }
+  }
+
+  return {
+    json: updatedJson,
+    revert,
+    error: null
+  }
+}
+
+/**
+ * Replace an existing item
+ * @param {JSON} json
+ * @param {Path} path
+ * @param {JSON} value
+ * @param {JSONPatchOptions} [options]
+ * @return {{json: JSON, revert: JSONPatchDocument}}
+ */
+export function replace (json, path, value, options) {
+  const oldValue = getIn(json, path)
+  const newValue = options.fromJSON(value, oldValue)
+
+  return {
+    json: setIn(json, path, newValue),
+    revert: [{
+      op: 'replace',
+      path: compileJSONPointer(path),
+      value: oldValue
+    }]
+  }
+}
+
+/**
+ * Remove an item or property
+ * @param {JSON} json
+ * @param {Path} path
+ * @param {JSONPatchOptions} [options]
+ * @return {{json: JSON, revert: JSONPatchDocument}}
+ */
+export function remove (json, path, options) {
+  const oldValue = getIn(json, path)
+
+  return {
+    json: deleteIn(json, path),
+    revert: [{
+      op: 'add',
+      path: compileJSONPointer(path),
+      value: options.toJSON(oldValue)
+    }]
+  }
+}
+
+/**
+ * @param {JSON} json
+ * @param {Path} path
+ * @param {JSON} value
+ * @param {JSONPatchOptions} [options]
+ * @return {{json: JSON, revert: JSONPatchDocument}}
+ * @private
+ */
+export function add (json, path, value, options) {
+  const resolvedPath = resolvePathIndex(json, path)
+  const parent = getIn(json, initial(path))
+  const parentIsArray = Array.isArray(parent)
+  const oldValue = parentIsArray
+      ? undefined
+      : getIn(json, resolvedPath)
+  const newValue = options.fromJSON(value, oldValue)
+
+  const updatedJson = parentIsArray
+      ? insertAt(json, resolvedPath, newValue)
+      : setIn(json, resolvedPath, newValue)
+
+  if (!parentIsArray && existsIn(json, resolvedPath)) {
+    return {
+      json: updatedJson,
+      revert: [{
+        op: 'replace',
+        path: compileJSONPointer(resolvedPath),
+        value: options.toJSON(oldValue)
+      }]
+    }
+  }
+  else {
+    return {
+      json: updatedJson,
+      revert: [{
+        op: 'remove',
+        path: compileJSONPointer(resolvedPath)
+      }]
+    }
+  }
+}
+
+/**
+ * Copy a value
+ * @param {JSON} json
+ * @param {Path} path
+ * @param {Path} from
+ * @param {JSONPatchOptions} [options]
+ * @return {{json: JSON, revert: JSONPatchDocument}}
+ * @private
+ */
+export function copy (json, path, from, options) {
+  const value = options.clone
+      ? options.clone(getIn(json, from))
+      : options.fromJSON(options.toJSON(getIn(json, from)), undefined)
+
+  return add(json, path, value, {
+    fromJSON: DEFAULT_OPTIONS.fromJSON,
+    toJSON: options.toJSON,
+    clone: options.clone
+  })
+}
+
+/**
+ * Move a value
+ * @param {JSON} json
+ * @param {Path} path
+ * @param {Path} from
+ * @param {JSONPatchOptions} [options]
+ * @return {{json: JSON, revert: JSONPatchDocument}}
+ * @private
+ */
+export function move (json, path, from, options) {
+  const resolvedPath = resolvePathIndex(json, path)
+  const parent = getIn(json, initial(path))
+  const parentIsArray = Array.isArray(parent)
+  const oldValue = getIn(json, path)
+  const value = getIn(json, from)
+
+  const removedJson = remove(json, from, options).json
+  const updatedJson = parentIsArray
+      ? insertAt(removedJson, resolvedPath, value)
+      : setIn(removedJson, resolvedPath, value)
+
+  if (oldValue !== undefined && !parentIsArray) {
+    // replaces an existing value in an object
+    return {
+      json: updatedJson,
+      revert: [
+        {
+          op: 'move',
+          from: compileJSONPointer(resolvedPath),
+          path: compileJSONPointer(from)
+        },
+        {
+          op: 'add',
+          path: compileJSONPointer(resolvedPath),
+          value: options.toJSON(oldValue)
+        }
+      ]
+    }
+  }
+  else {
+    return {
+      json: updatedJson,
+      revert: [
+        {
+          op: 'move',
+          from: compileJSONPointer(resolvedPath),
+          path: compileJSONPointer(from)
+        }
+      ]
+    }
+  }
+}
+
+/**
+ * Test whether the data contains the provided value at the specified path.
+ * Throws an error when the test fails.
+ * @param {JSON} json
+ * @param {Path} path
+ * @param {JSON} value
+ * @param {JSONPatchOptions} [options]
+ * @return {null | Error} Returns an error when the tests, returns null otherwise
+ */
+export function test (json, path, value, options) {
+  if (value === undefined) {
+    return new Error('Test failed, no value provided')
+  }
+
+  if (!existsIn(json, path)) {
+    return new Error('Test failed, path not found')
+  }
+
+  const actualValue = options.toJSON(getIn(json, path))
+  if (!isEqual(actualValue, value)) {
+    return new Error('Test failed, value differs')
+  }
+}
+
+/**
+ * Resolve the path of an index like '''
+ * @param {JSON} json
+ * @param {Path} path
+ * @returns {Path} Returns the resolved path
+ */
+export function resolvePathIndex (json, path) {
+  const parent = getIn(json, initial(path))
+
+  return (path[path.length - 1] === '-')
+      ? path.slice(0, path.length - 1).concat(parent.length)
+      : path
+}

src/utils/immutableJSONPatch.test.js

@@ -0,0 +1,373 @@
+import { immutableJSONPatch } from './immutableJSONPatch.js'
+import { expect } from './testUtils.js' // FIXME: replace jest with mocha tests, or move to jest
+
+const test = it // TODO: replace jest with mocha tests, or move to jest
+
+test('test toBe', () => {
+  const a = { x: 2 }
+  const b = { x: 2 }
+
+  // just to be sure toBe does what I think it does...
+  expect(a).toBe(a)
+  expect(b).not.toBe(a)
+  expect(b).toEqual(a)
+})
+
+test('jsonpatch add', () => {
+  const json = {
+    arr: [1,2,3],
+    obj: {a : 2}
+  }
+
+  const patch = [
+    {op: 'add', path: '/obj/b', value: {foo: 'bar'}}
+  ]
+
+  const result = immutableJSONPatch(json, patch)
+
+  expect(result.json).toEqual({
+    arr: [1,2,3],
+    obj: {a : 2, b: {foo: 'bar'}}
+  })
+  expect(result.revert).toEqual([
+    {op: 'remove', path: '/obj/b'}
+  ])
+  expect(result.json.arr).toBe(json.arr)
+})
+
+test('jsonpatch add: insert in matrix', () => {
+  const json = {
+    arr: [1,2,3],
+    obj: {a : 2}
+  }
+
+  const patch = [
+    {op: 'add', path: '/arr/1', value: 4}
+  ]
+
+  const result = immutableJSONPatch(json, patch)
+
+  expect(result.json).toEqual({
+    arr: [1,4,2,3],
+    obj: {a : 2}
+  })
+  expect(result.revert).toEqual([
+    {op: 'remove', path: '/arr/1'}
+  ])
+  expect(result.json.obj).toBe(json.obj)
+})
+
+test('jsonpatch add: append to matrix', () => {
+  const json = {
+    arr: [1,2,3],
+    obj: {a : 2}
+  }
+
+  const patch = [
+    {op: 'add', path: '/arr/-', value: 4}
+  ]
+
+  const result = immutableJSONPatch(json, patch)
+
+  expect(result.json).toEqual({
+    arr: [1,2,3,4],
+    obj: {a : 2}
+  })
+  expect(result.revert).toEqual([
+    {op: 'remove', path: '/arr/3'}
+  ])
+  expect(result.json.obj).toBe(json.obj)
+})
+
+test('jsonpatch remove', () => {
+  const json = {
+    arr: [1,2,3],
+    obj: {a : 4},
+    unchanged: {}
+  }
+
+  const patch = [
+    {op: 'remove', path: '/obj/a'},
+    {op: 'remove', path: '/arr/1'},
+  ]
+
+  const result = immutableJSONPatch(json, patch)
+
+  expect(result.json).toEqual({
+    arr: [1,3],
+    obj: {},
+    unchanged: {}
+  })
+  expect(result.revert).toEqual([
+    {op: 'add', path: '/arr/1', value: 2},
+    {op: 'add', path: '/obj/a', value: 4}
+  ])
+
+  // test revert
+  const result2 = immutableJSONPatch(result.json, result.revert)
+
+  expect(result2.json).toEqual(json)
+  expect(result2.revert).toEqual(patch)
+  expect(result.json.unchanged).toBe(json.unchanged)
+})
+
+test('jsonpatch replace', () => {
+  const json = {
+    arr: [1,2,3],
+    obj: {a : 4},
+    unchanged: {}
+  }
+
+  const patch = [
+    {op: 'replace', path: '/obj/a', value: 400},
+    {op: 'replace', path: '/arr/1', value: 200},
+  ]
+
+  const result = immutableJSONPatch(json, patch)
+
+  expect(result.json).toEqual({
+    arr: [1,200,3],
+    obj: {a: 400},
+    unchanged: {}
+  })
+  expect(result.revert).toEqual([
+    {op: 'replace', path: '/arr/1', value: 2},
+    {op: 'replace', path: '/obj/a', value: 4}
+  ])
+
+  // test revert
+  const result2 = immutableJSONPatch(result.json, result.revert)
+
+  expect(result2.json).toEqual(json)
+  expect(result2.revert).toEqual([
+    {op: 'replace', path: '/obj/a', value: 400},
+    {op: 'replace', path: '/arr/1', value: 200}
+  ])
+  expect(result.json.unchanged).toBe(json.unchanged)
+})
+
+test('jsonpatch copy', () => {
+  const json = {
+    arr: [1,2,3],
+    obj: {a : 4}
+  }
+
+  const patch = [
+    {op: 'copy', from: '/obj', path: '/arr/2'},
+  ]
+
+  const result = immutableJSONPatch(json, patch)
+
+  expect(result.json).toEqual({
+    arr: [1, 2, {a:4}, 3],
+    obj: {a: 4}
+  })
+  expect(result.revert).toEqual([
+    {op: 'remove', path: '/arr/2'}
+  ])
+
+  // test revert
+  const result2 = immutableJSONPatch(result.json, result.revert)
+
+  expect(result2.json).toEqual(json)
+  expect(result2.revert).toEqual([
+    {op: 'add', path: '/arr/2', value: {a: 4}}
+  ])
+  expect(result.json.obj).toBe(json.obj)
+  expect(result.json.arr[2]).toBe(json.obj)
+})
+
+test('jsonpatch move', () => {
+  const json = {
+    arr: [1,2,3],
+    obj: {a : 4},
+    unchanged: {}
+  }
+
+  const patch = [
+    {op: 'move', from: '/obj', path: '/arr/2'},
+  ]
+
+  const result = immutableJSONPatch(json, patch)
+
+  expect(result.error).toEqual(null)
+  expect(result.json).toEqual({
+    arr: [1, 2, {a:4}, 3],
+    unchanged: {}
+  })
+  expect(result.revert).toEqual([
+    {op: 'move', from: '/arr/2', path: '/obj'}
+  ])
+
+  // test revert
+  const result2 = immutableJSONPatch(result.json, result.revert)
+
+  expect(result2.json).toEqual(json)
+  expect(result2.revert).toEqual(patch)
+  expect(result.json.arr[2]).toBe(json.obj)
+  expect(result.json.unchanged).toBe(json.unchanged)
+})
+
+test('jsonpatch move and replace', () => {
+  const json = { a: 2, b: 3 }
+
+  const patch = [
+    {op: 'move', from: '/a', path: '/b'},
+  ]
+
+  const result = immutableJSONPatch(json, patch)
+
+  expect(result.json).toEqual({ b : 2 })
+  expect(result.revert).toEqual([
+    {op:'move', from: '/b', path: '/a'},
+    {op:'add', path:'/b', value: 3}
+  ])
+
+  // test revert
+  const result2 = immutableJSONPatch(result.json, result.revert)
+
+  expect(result2.json).toEqual(json)
+  expect(result2.revert).toEqual([
+    {op: 'remove', path: '/b'},
+    {op: 'move', from: '/a', path: '/b'}
+  ])
+})
+
+test('jsonpatch move and replace (nested)', () => {
+  const json = {
+    arr: [1,2,3],
+    obj: {a : 4},
+    unchanged: {}
+  }
+
+  const patch = [
+    {op: 'move', from: '/obj', path: '/arr'},
+  ]
+
+  const result = immutableJSONPatch(json, patch)
+
+  expect(result.json).toEqual({
+    arr: {a:4},
+    unchanged: {}
+  })
+  expect(result.revert).toEqual([
+    {op:'move', from: '/arr', path: '/obj'},
+    {op:'add', path:'/arr', value: [1,2,3]}
+  ])
+
+  // test revert
+  const result2 = immutableJSONPatch(result.json, result.revert)
+
+  expect(result2.json).toEqual(json)
+  expect(result2.revert).toEqual([
+    {op: 'remove', path: '/arr'},
+    {op: 'move', from: '/obj', path: '/arr'}
+  ])
+  expect(result.json.unchanged).toBe(json.unchanged)
+  expect(result2.json.unchanged).toBe(json.unchanged)
+})
+
+test('jsonpatch test (ok)', () => {
+  const json = {
+    arr: [1,2,3],
+    obj: {a : 4}
+  }
+
+  const patch = [
+    {op: 'test', path: '/arr', value: [1,2,3]},
+    {op: 'add', path: '/added', value: 'ok'}
+  ]
+
+  const result = immutableJSONPatch(json, patch)
+
+  expect(result.json).toEqual({
+    arr: [1,2,3],
+    obj: {a : 4},
+    added: 'ok'
+  })
+  expect(result.revert).toEqual([
+    {op: 'remove', path: '/added'}
+  ])
+})
+
+test('jsonpatch test (fail: path not found)', () => {
+  const json = {
+    arr: [1,2,3],
+    obj: {a : 4}
+  }
+
+  const patch = [
+    {op: 'test', path: '/arr/5', value: [1,2,3]},
+    {op: 'add', path: '/added', value: 'ok'}
+  ]
+
+  const result = immutableJSONPatch(json, patch)
+
+  // patch shouldn't be applied
+  expect(result.json).toEqual({
+    arr: [1,2,3],
+    obj: {a : 4}
+  })
+  expect(result.revert).toEqual([])
+  expect(result.error.toString()).toEqual('Error: Test failed, path not found')
+})
+
+test('jsonpatch test (fail: value not equal)', () => {
+  const json = {
+    arr: [1,2,3],
+    obj: {a : 4}
+  }
+
+  const patch = [
+    {op: 'test', path: '/obj', value: {a:4, b: 6}},
+    {op: 'add', path: '/added', value: 'ok'}
+  ]
+
+  const result = immutableJSONPatch(json, patch)
+
+  // patch shouldn't be applied
+  expect(result.json).toEqual({
+    arr: [1,2,3],
+    obj: {a : 4}
+  })
+  expect(result.revert).toEqual([])
+  expect(result.error.toString()).toEqual('Error: Test failed, value differs')
+})
+
+test('jsonpatch options', () => {
+  const json = {
+    arr: [1,2,3],
+    obj: {a : 2}
+  }
+
+  const patch = [
+    {op: 'add', path: '/obj/a', value: 4 }
+  ]
+  const result = immutableJSONPatch(json, patch, {
+    fromJSON: function (value, previousObject) {
+      return { value, previousObject }
+    },
+    toJSON: value => value
+  })
+  expect(result.json).toEqual({
+    arr: [1,2,3],
+    obj: {a : { value: 4, previousObject: 2 }}
+  })
+
+
+  const patch2 = [
+    {op: 'add', path: '/obj/b', value: 4 }
+  ]
+  const result2 = immutableJSONPatch(json, patch2, {
+    fromJSON: function (value, previousObject) {
+      return { value, previousObject }
+    },
+    toJSON: value => value
+  })
+  expect(result2.json).toEqual({
+    arr: [1,2,3],
+    obj: {a : 2, b: { value: 4, previousObject: undefined }}
+  })
+})
+
+// TODO: test all operations with JSONPatchOptions (not just add)

src/utils/jsonPointer.js

@@ -0,0 +1,24 @@
+/**
+ * Parse a JSON Pointer
+ * WARNING: this is not a complete implementation
+ * @param {string} pointer
+ * @return {Path}
+ */
+export function parseJSONPointer (pointer) {
+  const path = pointer.split('/')
+  path.shift() // remove the first empty entrypa
+
+  return path.map(p => p.replace(/~1/g, '/').replace(/~0/g, '~'))
+}
+
+/**
+ * Compile a JSON Pointer
+ * WARNING: this is not a complete implementation
+ * @param {Path} path
+ * @return {string}
+ */
+export function compileJSONPointer (path) {
+  return path
+      .map(p => '/' + String(p).replace(/~/g, '~0').replace(/\//g, '~1'))
+      .join('')
+}

src/utils/jsonPointer.test.js

@@ -0,0 +1,20 @@
+import {compileJSONPointer, parseJSONPointer} from './jsonPointer.js'
+import { expect } from './testUtils.js' // FIXME: replace jest with mocha tests, or move to jest
+
+const test = it // TODO: replace jest with mocha tests, or move to jest
+
+test('parseJSONPointer', () => {
+  expect(parseJSONPointer('/obj/a')).toEqual(['obj', 'a'])
+  expect(parseJSONPointer('/arr/-')).toEqual(['arr', '-'])
+  expect(parseJSONPointer('/foo/~1~0 ~0~1')).toEqual(['foo', '/~ ~/'])
+  expect(parseJSONPointer('/obj')).toEqual(['obj'])
+  expect(parseJSONPointer('/')).toEqual([''])
+  expect(parseJSONPointer('')).toEqual([])
+})
+
+test('compileJSONPointer', () => {
+  expect(compileJSONPointer(['foo', 'bar'])).toEqual('/foo/bar')
+  expect(compileJSONPointer(['foo', '/~ ~/'])).toEqual('/foo/~1~0 ~0~1')
+  expect(compileJSONPointer([''])).toEqual('/')
+  expect(compileJSONPointer([])).toEqual('')
+})

src/utils/testUtils.js

@@ -0,0 +1,29 @@
+import { deepStrictEqual, strictEqual, notStrictEqual, throws } from "assert"
+
+// TODO: integrate jest or switch to mocha
+// sort of mimicking jest
+export function expect (actual) {
+  return {
+    toEqual (expected) {
+      return deepStrictEqual(actual, expected)
+    },
+
+    toBe (expected) {
+      return strictEqual(actual, expected)
+    },
+
+    toBeUndefined () {
+      return strictEqual(actual, undefined)
+    },
+
+    toThrow (error) {
+      return throws(actual, error)
+    },
+
+    not: {
+      toBe (expected) {
+        return notStrictEqual(actual, expected)
+      }
+    }
+  }
+}

src/utils/typeUtils.js

@@ -0,0 +1,123 @@
+
+// TODO: unit test typeUtils.js
+
+/**
+ * Test whether a value is an Object (and not an Array!)
+ *
+ * @param {*} value
+ * @return {boolean}
+ */
+export function isObject (value) {
+  return typeof value === 'object' &&
+      value !== null &&
+      !Array.isArray(value) &&
+      (!value._meta || typeof value._meta.value === 'undefined')
+}
+
+/**
+ * Test whether a value is not an object or array, but null, number, string, or
+ * boolean.
+ * @param {*} value
+ * @return {boolean}
+ */
+export function isValue (value) {
+  return (value === null ||
+      typeof value === 'number' ||
+      typeof value === 'string' ||
+      typeof value === 'boolean')
+}
+
+/**
+ * Test whether a value is an Object or an Array
+ *
+ * @param {*} value
+ * @return {boolean}
+ */
+export function isObjectOrArray (value) {
+  return typeof value === 'object' && value !== null
+}
+
+/**
+ * Get the JSON node type of a value: 'array', 'object', or 'value'
+ * @param {*} json
+ * @returns {string}
+ */
+export function getJSONNodeType (json) {
+  return Array.isArray(json)
+    ? 'array'
+    : json && typeof json === 'object'
+      ? 'object'
+      : 'value'
+}
+
+/**
+ * Get the type of a value
+ * @param {*} value
+ * @return {String} type
+ */
+export function valueType(value) {
+  if (value === null) {
+    return 'null'
+  }
+  if (value === undefined) {
+    return 'undefined'
+  }
+  if (typeof value === 'number') {
+    return 'number'
+  }
+  if (typeof value === 'string') {
+    return 'string'
+  }
+  if (typeof value === 'boolean') {
+    return 'boolean'
+  }
+  if (value instanceof RegExp) {
+    return 'regexp'
+  }
+  if (Array.isArray(value)) {
+    return 'array'
+  }
+
+  return 'object'
+}
+
+/**
+ * Test whether a text contains a url (matches when a string starts
+ * with 'http://*' or 'https://*' and has no whitespace characters)
+ * @param {String} text
+ */
+const isUrlRegex = /^https?:\/\/\S+$/
+export function isUrl (text) {
+  return (typeof text === 'string') && isUrlRegex.test(text)
+}
+
+/**
+ * Convert contents of a string to the correct JSON type. This can be a string,
+ * a number, a boolean, etc
+ * @param {String} str
+ * @return {*} castedStr
+ * @private
+ */
+export function stringConvert (str) {
+  const num = Number(str)           // will nicely fail with '123ab'
+  const numFloat = parseFloat(str)  // will nicely fail with '  '
+
+  if (str === '') {
+    return ''
+  }
+  else if (str === 'null') {
+    return null
+  }
+  else if (str === 'true') {
+    return true
+  }
+  else if (str === 'false') {
+    return false
+  }
+  else if (!isNaN(num) && !isNaN(numFloat)) {
+    return num
+  }
+  else {
+    return str
+  }
+}

src/utils/typeUtils.test.js

@@ -0,0 +1,13 @@
+import { getJSONNodeType } from './typeUtils.js'
+import { expect } from './testUtils.js' // FIXME: replace jest with mocha tests, or move to jest
+
+const test = it // TODO: replace jest with mocha tests, or move to jest
+
+test('test getJsonType', () => {
+  expect(getJSONNodeType([])).toEqual('array')
+  expect(getJSONNodeType({})).toEqual('object')
+  expect(getJSONNodeType(null)).toEqual('value')
+  expect(getJSONNodeType(2)).toEqual('value')
+  expect(getJSONNodeType('hello')).toEqual('value')
+  expect(getJSONNodeType('hello')).toEqual('value')
+})