Created immutability function `insertAt`

src/jsonData.js

@@ -3,7 +3,7 @@
  * All functions are pure and don't mutate the JSONData.
  */
 
-import { setIn, updateIn, getIn, deleteIn } from './utils/immutabilityHelpers'
+import { setIn, updateIn, getIn, deleteIn, insertAt } from './utils/immutabilityHelpers'
 import { isObject } from  './utils/typeUtils'
 import isEqual from 'lodash/isEqual'
 
@@ -336,18 +336,10 @@ export function add (data, path, value, options) {
 
   let updatedData
   if (parent.type === 'Array') {
-    // TODO: create an immutable helper function to insert an item in an Array
-    updatedData = updateIn(data, dataPath.concat('items'), (items) => {
-      const index = parseInt(prop)
-      const updatedItems = items.slice(0)
-
-      updatedItems.splice(index, 0, value)
-
-      return updatedItems
-    })
+      updatedData = insertAt(data, dataPath.concat('items', prop), value)
   }
   else { // parent.type === 'Object'
-    // TODO: create an immutable helper function to append an item to an Array
+    // TODO: create an immutable helper function to update a property in an Object
     updatedData = updateIn(data, dataPath.concat('props'), (props) => {
       const newProp = { name: prop, value }
 

src/utils/immutabilityHelpers.js

@@ -150,3 +150,27 @@ export function deleteIn (object, path) {
     return updatedObject
   }
 }
+
+/**
+ * Insert a new item in an array
+ * @param {Array} array
+ * @param {Path} path
+ * @param {*} value
+ * @return {Array}
+ */
+export function insertAt (array, path, value) {
+  const parentPath = path.slice(0, path.length - 1)
+  const index = path[path.length - 1]
+
+  return updateIn(array, parentPath, (items) => {
+    if (!Array.isArray(items)) {
+      throw new TypeError('Array expected at path ' + JSON.stringify(parentPath))
+    }
+
+    const updatedItems = items.slice(0)
+
+    updatedItems.splice(index, 0, value)
+
+    return updatedItems
+  })
+}

test/immutabilityHelpers.test.js

@@ -1,5 +1,5 @@
 import test from 'ava';
-import { getIn, setIn, updateIn, deleteIn } from '../src/utils/immutabilityHelpers'
+import { getIn, setIn, updateIn, deleteIn, insertAt } from '../src/utils/immutabilityHelpers'
 
 
 test('getIn', t => {
@@ -269,3 +269,10 @@ test('deleteIn non existing path', t => {
   const updated = deleteIn(obj, ['a', 'b'])
   t.truthy (updated === obj)
 })
+
+test('insertAt', t => {
+  const obj = { a: [1,2,3]}
+
+  const updated = insertAt(obj, ['ab', '2'], 8)
+  t.deepEqual(updated, {a: [1,2,8,3]})
+})