Props working properly now (though solution is half mutable)

src/App.svelte

@@ -8,33 +8,33 @@
 	export let searchText = ''
 
 	let json = {
-		'array': [1, 2, 3, {
-			name: 'Item ' + 2,
-			id: String(2),
-			index: 2,
-			time: new Date().toISOString(),
-			location: {
-				latitude: 1.23,
-				longitude: 23.44,
-				coordinates: [23.44, 1.23]
-			},
-		}],
+		// 'array': [1, 2, 3, {
+		// 	name: 'Item ' + 2,
+		// 	id: String(2),
+		// 	index: 2,
+		// 	time: new Date().toISOString(),
+		// 	location: {
+		// 		latitude: 1.23,
+		// 		longitude: 23.44,
+		// 		coordinates: [23.44, 1.23]
+		// 	},
+		// }],
 		'boolean': true,
 		'color': '#82b92c',
 		'null': null,
 		'number': 123,
-		'object': {'a': 'b', 'c': 'd', nested: {
-			name: 'Item ' + 2,
-			id: String(2),
-			index: 2,
-			time: new Date().toISOString(),
-			location: {
-				latitude: 1.23,
-				longitude: 23.44,
-				coordinates: [23.44, 1.23]
-			},
-		}},
-		'string': 'Hello World'
+		// 'object': {'a': 'b', 'c': 'd', nested: {
+		// 	name: 'Item ' + 2,
+		// 	id: String(2),
+		// 	index: 2,
+		// 	time: new Date().toISOString(),
+		// 	location: {
+		// 		latitude: 1.23,
+		// 		longitude: 23.44,
+		// 		coordinates: [23.44, 1.23]
+		// 	},
+		// }},
+		// 'string': 'Hello World'
 	}
 
 	let uniDirectionalValue = 'test uni directional flow in Svelte';

src/JSONNode.svelte

@@ -4,9 +4,8 @@
   import { SEARCH_PROPERTY, SEARCH_VALUE } from './search'
   import classnames from 'classnames'
   import { isUrl, valueType } from './utils/typeUtils'
-  import { escapeHTML } from './utils/stringUtils'
-  import uniqueId from 'lodash/uniqueId.js'
-  import remove from 'lodash/remove.js'
+  import { escapeHTML } from './utils/stringUtils.js'
+  import { createUpdateProps } from './utils/updateProps.js'
 
   export let key = 'root'
   export let value
@@ -18,32 +17,18 @@
   const DEFAULT_LIMIT = 10000
   const escapeUnicode = false // TODO: pass via options
 
+  // create lazy, memoized updateProps function
+  let updateProps = function lazyUpdateProps (value) {
+    updateProps = createUpdateProps()
+    return updateProps(value)
+  }
+
   let limit = DEFAULT_LIMIT
 
   $: type = valueType (value)
 
-
-  function getOrCreateId (childKey) {
-    if (ids === undefined) {
-      ids = {}
-    }
-
-    if (ids[childKey] === undefined) {
-      ids[childKey] = uniqueId()
-    }
-
-    return ids[childKey]
-  }
-
-  // FIXME: this should not be needed, use Svelte notation for looping over an object
-  let ids = undefined
   $: props = type === 'object'
-    ? Object.keys(value).map(childKey => {
-      return {
-        id: getOrCreateId(childKey),
-        key: childKey
-      }
-    })
+    ? updateProps(value)
     : undefined
 
   $: limited = type === 'array' && value.length > limit
@@ -88,9 +73,10 @@
         }
       })
 
-      if (ids !== undefined) {
-        ids[newChildKey] = ids[oldChildKey]
-        delete ids[oldChildKey]
+      const index = props.findIndex(item => item.key === oldChildKey)
+      if (index !== -1) {
+        // FIXME: make immutable (not possible as long as prevProps is stored in updateProps
+        props[index].key = newChildKey
       }
 
       onChangeValue(updatedValue, key)

src/utils/updateProps.js

@@ -0,0 +1,37 @@
+import { isObject } from './typeUtils.js'
+import uniqueId from 'lodash/uniqueId.js'
+
+export function createUpdateProps () {
+  let prevProps = undefined
+
+  return function updateProps (value) {
+    // TODO: optimize. check if value is the same as prevValue, if so, don't do anything
+
+    if (isObject(value)) {
+      const props = prevProps
+        ? prevProps.filter(item => value[item.key] !== undefined) // copy the props that still exist
+        : []
+
+      // process added props
+      const prevKeys = new Set(props.map(item => item.key)) // TODO: this is inefficient, creating a set. cache this set?
+
+      console.log('updateProps', { value, prevProps, props})
+
+      Object.keys(value).forEach(key => {
+        if (!prevKeys.has(key)) {
+          console.log('add key', key)
+          props.push({
+            id: uniqueId(),
+            key
+          })
+        }
+      })
+
+      prevProps = props
+      return props
+    } else {
+      prevProps = undefined
+      return undefined
+    }
+  }
+}

src/utils/updateProps.test.js

@@ -0,0 +1,20 @@
+import { createUpdateProps } from './updateProps.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('updateProps (1)', () => {
+  const updateProps = createUpdateProps()
+
+  expect(updateProps({b: 2}).map(item => item.key)).toEqual(['b'])
+
+  const result2 = updateProps({a: 1, b: 2})
+  expect(result2.map(item => item.key)).toEqual(['b', 'a'])
+  expect(result2[0].id).toEqual('1')
+})
+
+test('updateProps (2)', () => {
+  const updateProps = createUpdateProps()
+  const result1 = updateProps({a: 1, b: 2})
+  expect(updateProps({a: 1, b: 2})).toEqual(result1)
+})