Add call helper (#380)

* Add call helper

* add test

* add readme

* add export

README.md

@@ -67,6 +67,7 @@ Watch a free video overview presented by EmberMap:
       - [`compact`](#compact)
       - [`contains`](#contains)
       - [`append`](#append)
+      - [`call`](#call)
       - [`chunk`](#chunk)
       - [`without`](#without)
       - [`shuffle`](#shuffle)
@@ -550,6 +551,19 @@ Appends the given arrays and/or values into a single flat array.
 
 **[⬆️ back to top](#table-of-contents)**
 
+#### `call`
+Calls the given function with arguments
+
+```hbs
+{{#each (call (fn this.callMeWith @daysInMonth) as |week|}}
+  {{#each week as |day|}}
+    {{day}}
+  {{/each}}
+{{/each}}
+```
+
+**[⬆️ back to top](#table-of-contents)**
+
 #### `chunk`
 Returns the given array split into sub-arrays the length of the given value.
 

addon/helpers/call.js

@@ -0,0 +1,27 @@
+import Helper from '@ember/component/helper';
+
+/**
+ * Calls a function passed within a template and returns its value.
+ * In order to pass arguments to the function being called, you must
+ * curry the function using the `fn` helper.
+ *
+ ```example
+    <div data-metrics={{call (fn this.myMetrics (hash item=@item))}}
+  ```
+ *
+ * @function apply
+ * @param {Array<Function>} fn - The function to be called
+ * @param {*=} thisArg - An optional `this` context
+ */
+export function call([fn, thisArg]) {
+    if (fn) {
+        if (thisArg) {
+            return fn.apply(thisArg);
+        } else {
+            return fn();
+        }
+    }
+}
+
+export default Helper.helper(call);
+

app/helpers/call.js

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

tests/integration/helpers/call-test.js

@@ -0,0 +1,33 @@
+import { module, test } from 'qunit';
+import { setupRenderingTest } from 'ember-qunit';
+import { render } from '@ember/test-helpers';
+import hbs from 'htmlbars-inline-precompile';
+
+module('Integration | Helper | call', function (hooks) {
+    setupRenderingTest(hooks);
+
+    test('it renders a function return value with curried arguments', async function (assert) {
+        this.fn = function (value) {
+            return value.toUpperCase();
+        };
+
+        await render(hbs`{{call (fn this.fn "foo")}}`);
+
+        assert.dom(this.element).hasText('FOO');
+    });
+
+    test('it calls a function with this binding', async function (assert) {
+        this.that = {
+            value: 'foo',
+        };
+
+        this.fn = function () {
+            return this.value.toUpperCase();
+        };
+
+        await render(hbs`{{call this.fn this.that}}`);
+
+        assert.dom(this.element).hasText('FOO');
+    });
+});
+