Fix changing property name not working for arrays and objects

src/App.svelte

@@ -7,7 +7,7 @@
 
 	export let searchText = ''
 
-	let json = {
+	export let json = {
 		'array': [1, 2, 3, {
 			name: 'Item ' + 2,
 			id: String(2),
@@ -102,7 +102,7 @@
 	}
 
 	function handleChangeValue (value, key) {
-		console.log('App handleChangeValue')
+		console.log('App handleChangeValue', value, key)
 		json = value
 	}
 

src/JSONNode.svelte

@@ -5,7 +5,7 @@
   import classnames from 'classnames'
   import { isUrl, stringConvert, valueType } from './utils/typeUtils'
   import { escapeHTML } from './utils/stringUtils.js'
-  import { createUpdateProps } from './utils/updateProps.js'
+  import { updateProps } from './utils/updateProps.js'
   import { unescapeHTML } from './utils/stringUtils'
 
   export let key = undefined
@@ -18,19 +18,18 @@
   const DEFAULT_LIMIT = 100
   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)
 
-  $: props = type === 'object'
-    ? updateProps(value)
-    : undefined
+  let prevValue = undefined
+  let props = updateProps(value)
+
+  $: if (value !== prevValue) {
+    prevValue = value
+
+    props = updateProps(value, props)
+  }
 
   $: limited = type === 'array' && value.length > limit
 
@@ -96,8 +95,15 @@
 
       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
+        // we use splice here to replace the old key with the new new one 
+        // already without Svelte noticing it (no assignment), so we prevent
+        // a needless render. We keep the same id, so the child HTML will be
+        // reused
+        // TODO: is there a better way to do this?
+        props.splice(index, 1, {
+          id: props[index].id,
+          key: newChildKey
+        })
       }
 
       onChangeValue(updatedValue, key)

src/utils/updateProps.js

@@ -1,34 +1,26 @@
 import { isObject } from './typeUtils.js'
 import uniqueId from 'lodash/uniqueId.js'
 
-export function createUpdateProps () {
-  let prevProps = undefined
+export function updateProps (value, prevProps) {
+  if (isObject(value)) {
+    // copy the props that still exist
+    const props = prevProps
+      ? prevProps.filter(item => value[item.key] !== undefined) 
+      : []
 
-  return function updateProps (value) {
-    // TODO: optimize. check if value is the same as prevValue, if so, don't do anything
+    // add new props
+    const prevKeys = new Set(props.map(item => item.key))
+    Object.keys(value).forEach(key => {
+      if (!prevKeys.has(key)) {
+        props.push({
+          id: uniqueId(),
+          key
+        })
+      }
+    })
 
-    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?
-
-      Object.keys(value).forEach(key => {
-        if (!prevKeys.has(key)) {
-          props.push({
-            id: uniqueId(),
-            key
-          })
-        }
-      })
-
-      prevProps = props
-      return props
-    } else {
-      prevProps = undefined
-      return undefined
-    }
+    return props
+  } else {
+    return undefined
   }
 }