Pick Helper (#366)

* Introduce pick object helper

* Alphabetize object helpers in README

README.md

@@ -78,11 +78,12 @@ Watch a free video overview presented by EmberMap:
       - [`previous`](#previous)
       - [`has-previous`](#has-previous)
     - [Object helpers](#object-helpers)
+      - [`entries`](#entries)
+      - [`from-entries`](#from-entries)
       - [`group-by`](#group-by)
       - [`keys`](#keys)
+      - [`pick`](#pick)
       - [`values`](#values)
-      - [`entries`](#entries)
-      - [`from-entries`](#from-entries)
     - [Math helpers](#math-helpers)
       - [`inc`](#inc)
       - [`dec`](#dec)
@@ -669,6 +670,45 @@ parameter, `useDeepEqual`, to flag whether a deep equal comparison should be per
 
 ### Object helpers
 
+#### `entries`
+Returns an array of a given object's own enumerable string-keyed property `[key, value]` pairs
+
+```hbs
+  {{#each (entries object) as |entry|}}
+    {{get entry 0}}:{{get entry 1}}
+  {{/each}}
+```
+
+You can pair it with other array helpers too. For example
+
+```hbs
+  {{#each (sort-by myOwnSortByFunction (entries myObject)) as |entry|}}
+    {{get entry 0}}
+  {{/each}}`);
+```
+
+**[⬆️ back to top](#table-of-contents)**
+
+#### `from-entries`
+Converts a two-dimensional array of `[key, value]` pairs into an Object
+
+```hbs
+  {{#each-in (from-entries entries) as |key value|}}
+    {{key}}:{{value}}
+  {{/each}}
+```
+
+You can pair it with other array helpers too. For example, to copy only
+properties with non-falsey values:
+
+```hbs
+  {{#each-in (from-entries (filter-by "1" (entries myObject))) as |k v|}}
+    {{k}}: {{v}}
+  {{/each-in}}`);
+```
+
+**[⬆️ back to top](#table-of-contents)**
+
 #### `group-by`
 Returns an object where the keys are the unique values of the given property, and the values are an array with all items of the array that have the same value of that property.
 
@@ -701,6 +741,27 @@ Returns an array of keys of given object.
 
 **[⬆️ back to top](#table-of-contents)**
 
+#### `pick`
+Receives an object and picks a specified path off of it to pass on. Intended for use with `{{on}}` modifiers placed on form elements.
+
+```hbs
+  <input
+    ...
+    {{on 'input' (pipe (pick 'target.value') this.onInput)}}
+  />
+```
+
+It also supports an optional second argument to make common usage more ergonomic.
+
+```hbs
+  <input
+    ...
+    {{on 'input' (pick 'target.value' this.onInput)}}
+  />
+```
+
+**[⬆️ back to top](#table-of-contents)*
+
 #### `values`
 Returns an array of values from the given object.
 
@@ -715,46 +776,7 @@ Returns an array of values from the given object.
 {{/with}}
 ```
 
-**[⬆️ back to top](#table-of-contents)**
-
-#### `entries`
-Returns an array of a given object's own enumerable string-keyed property `[key, value]` pairs
-
-```hbs
-  {{#each (entries object) as |entry|}}
-    {{get entry 0}}:{{get entry 1}}
-  {{/each}}
-```
-
-You can pair it with other array helpers too. For example
-
-```hbs
-  {{#each (sort-by myOwnSortByFunction (entries myObject)) as |entry|}}
-    {{get entry 0}}
-  {{/each}}`);
-```
-
-**[⬆️ back to top](#table-of-contents)**
-
-#### `from-entries`
-Converts a two-dimensional array of `[key, value]` pairs into an Object
-
-```hbs
-  {{#each-in (from-entries entries) as |key value|}}
-    {{key}}:{{value}}
-  {{/each}}
-```
-
-You can pair it with other array helpers too. For example, to copy only
-properties with non-falsey values:
-
-```hbs
-  {{#each-in (from-entries (filter-by "1" (entries myObject))) as |k v|}}
-    {{k}}: {{v}}
-  {{/each-in}}`);
-```
-
-**[⬆️ back to top](#table-of-contents)**
+**[⬆️ back to top](#table-of-contents)*
 
 ---
 

addon/helpers/pick.js

@@ -0,0 +1,14 @@
+import { helper } from '@ember/component/helper';
+import { get } from '@ember/object';
+
+export default helper(function event([path, action]/*, hash*/) {
+  return function(event) {
+    let value = get(event, path);
+
+    if (!action) {
+      return value;
+    }
+
+    action(value);
+  };
+});

app/helpers/pick.js

@@ -0,0 +1 @@
+export { default, pick } from 'ember-composable-helpers/helpers/pick';

tests/integration/helpers/pick-test.js

@@ -0,0 +1,44 @@
+import { module, test } from 'qunit';
+import { setupRenderingTest } from 'ember-qunit';
+import { click, render } from '@ember/test-helpers';
+import hbs from 'htmlbars-inline-precompile';
+
+module('Integration | Helper | pick', function(hooks) {
+  setupRenderingTest(hooks);
+
+  test("Works when used with {{on}} modifier and pipe", async function(assert) {
+    assert.expect(1);
+
+    this.set('onFocus', function(value) {
+      assert.equal(value, 'pizza party', 'The action receives the correct value');
+    })
+
+    await render(hbs`
+      <input
+        id="test-input"
+        value="pizza party"
+        {{on 'focusin' (pipe (pick 'target.value') this.onFocus)}}
+      />
+    `);
+
+    await click('#test-input');
+  });
+
+  test("Shorthand works when used with {{on}} modifier and optional action is provided", async function(assert) {
+    assert.expect(1);
+
+    this.set('onFocus', function(value) {
+      assert.equal(value, 'pizza party', 'The action receives the correct value');
+    })
+
+    await render(hbs`
+      <input
+        id="test-input"
+        value="pizza party"
+        {{on 'focusin' (pick 'target.value' this.onFocus)}}
+      />
+    `);
+
+    await click('#test-input');
+  });
+});