Initial implementation of emberjs/rfcs#415

This is the initial implementation of
[emberjs/rfcs#415](https://emberjs.github.io/rfcs/0415-render-element-modifiers.html).

It currently depends on
[ember-modifier-manager-polyfill](https://github.com/rwjblue/ember-modifier-manager-polyfill)
in order to support Ember versions prior to 3.8 (should work back to at
least 2.12).

Author: Robert Jackson

addon/.gitkeep

@@ -0,0 +1,17 @@
+import Ember from 'ember';
+
+export default Ember._setModifierManager(
+  () => ({
+    createModifier() {},
+
+    installModifier(_state, element, args) {
+      let [fn, ...positional] = args.positional;
+
+      fn(element, positional, args.named);
+    },
+
+    updateModifier() {},
+    destroyModifier() {},
+  }),
+  class DidInsertModifier {}
+);

addon/modifiers/did-insert.js

@@ -0,0 +1,22 @@
+import Ember from 'ember';
+
+export default Ember._setModifierManager(
+  () => ({
+    createModifier() {
+      return { element: null };
+    },
+    installModifier(state, element) {
+      // save element into state bucket
+      state.element = element;
+    },
+
+    updateModifier({ element }, args) {
+      let [fn, ...positional] = args.positional;
+
+      fn(element, positional, args.named);
+    },
+
+    destroyModifier() {},
+  }),
+  class DidUpdateModifier {}
+);

addon/modifiers/did-update.js

@@ -0,0 +1,22 @@
+import Ember from 'ember';
+
+export default Ember._setModifierManager(
+  () => ({
+    createModifier() {
+      return { element: null };
+    },
+
+    installModifier(state, element) {
+      state.element = element;
+    },
+
+    updateModifier() {},
+
+    destroyModifier({ element }, args) {
+      let [fn, ...positional] = args.positional;
+
+      fn(element, positional, args.named);
+    },
+  }),
+  class WillDestroyModifier {}
+);

addon/modifiers/will-destroy.js

@@ -0,0 +1 @@
+export { default } from '@ember/render-modifiers/modifiers/did-insert';

app/.gitkeep

@@ -0,0 +1 @@
+export { default } from '@ember/render-modifiers/modifiers/did-update';

app/modifiers/did-insert.js

@@ -0,0 +1 @@
+export { default } from '@ember/render-modifiers/modifiers/will-destroy';

app/modifiers/did-update.js

@@ -0,0 +1,52 @@
+import { module, test } from 'qunit';
+import { setupRenderingTest } from 'ember-qunit';
+import { render } from '@ember/test-helpers';
+import hbs from 'htmlbars-inline-precompile';
+
+module('Integration | Modifier | did-insert', function(hooks) {
+  setupRenderingTest(hooks);
+
+  test('it basically works', async function(assert) {
+    assert.expect(2);
+
+    this.someMethod = element => {
+      assert.equal(element.tagName, 'DIV', 'correct element tagName');
+      assert.dom(element).hasAttribute('data-foo', 'some-thing');
+    };
+    await render(hbs`<div data-foo="some-thing" {{did-insert this.someMethod}}></div>`);
+  });
+
+  test('it can accept arguments', async function(assert) {
+    assert.expect(4);
+
+    this.someMethod = (element, positional, named) => {
+      assert.equal(element.tagName, 'DIV', 'correct element tagName');
+      assert.dom(element).hasAttribute('data-foo', 'some-thing');
+
+      assert.deepEqual(named, { some: 'hash-value' }, 'named args match');
+      assert.deepEqual(positional, ['some-positional-value'], 'positional args match');
+    };
+
+    await render(
+      hbs`<div data-foo="some-thing" {{did-insert this.someMethod "some-positional-value" some="hash-value"}}></div>`
+    );
+  });
+
+  test('it is not invoked again when arguments change', async function(assert) {
+    assert.expect(4);
+
+    this.someMethod = (element, positional, named) => {
+      assert.equal(element.tagName, 'DIV', 'correct element tagName');
+      assert.dom(element).hasAttribute('data-foo', 'some-thing');
+
+      assert.deepEqual(named, {}, 'named args match');
+      assert.deepEqual(positional, ['initial'], 'positional args match');
+    };
+
+    this.set('firstArg', 'initial');
+    await render(
+      hbs`<div data-foo="some-thing" {{did-insert this.someMethod this.firstArg}}></div>`
+    );
+    this.set('firstArg', 'updated');
+  });
+});

app/modifiers/will-destroy.js

@@ -0,0 +1,27 @@
+import { module, test } from 'qunit';
+import { setupRenderingTest } from 'ember-qunit';
+import { render } from '@ember/test-helpers';
+import hbs from 'htmlbars-inline-precompile';
+
+module('Integration | Modifier | did-update', function(hooks) {
+  setupRenderingTest(hooks);
+
+  test('it basically works', async function(assert) {
+    assert.expect(4);
+
+    this.someMethod = (element, positional, named) => {
+      assert.equal(element.tagName, 'DIV', 'correct element tagName');
+      assert.dom(element).hasAttribute('data-foo', 'some-thing');
+
+      assert.deepEqual(named, {}, 'named args match');
+      assert.deepEqual(positional, ['update'], 'positional args match');
+    };
+
+    this.set('boundValue', 'initial');
+    await render(
+      hbs`<div data-foo="some-thing" {{did-update this.someMethod this.boundValue}}></div>`
+    );
+
+    this.set('boundValue', 'update');
+  });
+});