Minimize rerender from new Mobiledoc

Move the editor destroy/setup flow into willRender and didRender.
Compare a new mobiledoc to the local mobiledoc and the upstream one
before destroying and recreating the editor.

Refs #42

addon/components/mobiledoc-editor/component.js

@@ -146,15 +146,31 @@ export default Component.extend({
     return Ember.A([]);
   }),
 
-  editor: computed('mobiledoc', 'isEditingDisabled', function() {
-    if (this._lastEditor) {
-      this._lastEditor.destroy();
-      this._lastEditor = null;
+  willRender() {
+    // Use a default mobiledoc. If there are no changes, then return
+    // early.
+    let mobiledoc = this.get('mobiledoc') || EMPTY_MOBILEDOC;
+    if (
+      (
+        (this._localMobiledoc && this._localMobiledoc === mobiledoc) ||
+        (this._upstreamMobiledoc && this._upstreamMobiledoc === mobiledoc)
+      ) && (this._lastIsEditingDisabled === this.get('isEditingDisabled'))
+    ) {
+      // No change to mobiledoc, no need to recreate the editor
+      return;
+    }
+    this._lastIsEditingDisabled = this.get('isEditingDisabled');
+    this._upstreamMobiledoc = mobiledoc;
+    this._localMobiledoc = null;
+
+    // Teardown any old editor that might be around.
+    let editor = this.get('editor');
+    if (editor) {
+      editor.destroy();
     }
-    let editor;
-    let mobiledoc = this.get('mobiledoc');
-    let editorOptions = this.get('editorOptions');
 
+    // Create a new editor.
+    let editorOptions = this.get('editorOptions');
     editorOptions.mobiledoc = mobiledoc;
     editorOptions.cardOptions = {
       [ADD_HOOK]: ({env, options, payload}, isEditing=false) => {
@@ -178,8 +194,10 @@ export default Component.extend({
           editor,
           postModel: env.postModel
         });
-        Ember.run.schedule('afterRender', () => {
-          this.get('componentCards').pushObject(card);
+        Ember.run.join(() => {
+          Ember.run.schedule('afterRender', () => {
+            this.get('componentCards').pushObject(card);
+          });
         });
         return { card, element };
       },
@@ -192,15 +210,18 @@ export default Component.extend({
     editor = new window.Mobiledoc.Editor(editorOptions);
     editor.on('update', () => {
       let updatedMobileDoc = editor.serialize();
-      this.sendAction('on-change', updatedMobileDoc);
+      this._localMobiledoc = updatedMobileDoc;
+      Ember.run.join(() => {
+        this.sendAction('on-change', updatedMobileDoc);
+      });
     });
     editor.cursorDidChange(() => {
       if (this.isDestroyed) { return; }
 
       const markupTags = arrayToMap(editor.markupsInSelection, 'tagName');
       const sectionTags = arrayToMap(editor.activeSections, 'tagName');
 
-      Ember.run(() => {
+      Ember.run.join(() => {
         this.set('activeMarkupTagNames', markupTags);
         this.set('activeSectionTagNames', sectionTags);
       });
@@ -215,15 +236,13 @@ export default Component.extend({
     if (this.get('isEditingDisabled')) {
       editor.disableEditing();
     }
-    this._lastEditor = editor;
-    return editor;
-  }),
+    this.set('editor', editor);
+  },
 
   didRender() {
     let editor = this.get('editor');
-    let editorElement = this.$('.mobiledoc-editor__editor')[0];
-    if (this._renderedEditor !== editor) {
-      this._renderedEditor = editor;
+    if (!editor.hasRendered) {
+      let editorElement = this.$('.mobiledoc-editor__editor')[0];
       editor.render(editorElement);
     }
   },

tests/integration/components/mobiledoc-editor/component-test.js

@@ -66,6 +66,35 @@ test('it boots mobiledoc editor with mobiledoc', function(assert) {
   );
 });
 
+test('it does not update the editor when the same mobiledoc is set', function(assert) {
+  assert.expect(2);
+  let mobiledoc = simpleMobileDoc('Howdy');
+  let editor;
+  let createdEditors = 0;
+
+  this.set('mobiledoc', mobiledoc);
+  this.register('component:gather-editor', Ember.Component.extend({
+    didRender() {
+      createdEditors++;
+      editor = this.get('editor');
+    }
+  }));
+  this.render(hbs`
+    {{#mobiledoc-editor mobiledoc=(readonly mobiledoc)
+                        on-change=(action (mut mobiledoc)) as |editor|}}
+      {{gather-editor editor=editor.editor}}
+    {{/mobiledoc-editor}}
+  `);
+
+  assert.equal(createdEditors, 1, 'initial editor created');
+
+  editor.run((postEditor) => {
+    postEditor.insertText(editor.range.tail, 'Friend');
+  });
+
+  assert.equal(createdEditors, 1, 'editor maintained');
+});
+
 test('it updates the editor when the mobiledoc changes', function(assert) {
   assert.expect(2);
   let mobiledoc1 = simpleMobileDoc('Howdy');