killerbytes · March 30, 2017 12:17 · Mar 30, 2017 · Jul 2, 2016
diff --git a/controllers.application.js b/controllers.application.js
@@ -60,7 +60,19 @@ DS.PromiseArray.reopen({
    * @return {Array}
    */
   filterAsync(asyncFn) {
-    return [42];
+    var result = [];
+
+    this.map(i=>{
+      asyncFn(i).then(res=>{
+         if(res) result.push(i);
+      })
+    })
+
+    var request = new Ember.RSVP.Promise(resolve=>{
+	    resolve(result);
+  	});    
+
+		return DS.PromiseArray.create({ promise: request });    
   }
 });
 

diff --git a/controllers.application.js b/controllers.application.js
@@ -0,0 +1,85 @@
+import Ember from 'ember';
+import DS from 'ember-data';
+
+/**
+ * Returns true iff the number passed in is even
+ * @param {Number} x
+ * @return {Boolean}
+ */
+function isEven(x) {
+  return x % 2 == 0;
+}
+
+/**
+ * Returns a Promise which resolves to true if the number passed in is even,
+ * and resolves to false otherwise
+ * @param {Number} x
+ * @return {Promise<Boolean>}
+ */
+function isEvenAsync(x) {
+  return new Ember.RSVP.Promise(function(resolve) {
+    let result = isEven(x);
+    resolve(result);
+  });
+}
+
+/* A DS.PromiseArray acts like both an Array and a promise.
+ * Have a look at its documentation:
+ * - http://emberjs.com/api/data/classes/DS.PromiseArray.html
+ * Once the underlying promise of the DS.PromiseArray resolves, its
+ * `content` property is set to the resulting value of that promise,
+ * (which should be an Array). This Array can then be used, e.g. in a template.
+ *
+ * DS.PromiseArray has a built-in method `filter` (inherited from Ember.ArrayProxy).
+ * This method takes a single parameter, a function `fn`, which takes a single value
+ * and returns a Boolean.
+ * Before the underlying promise of the PromiseArray has resolved, applying `filter`
+ * gives an empty Array.
+ * Once the underlying promise of the PromiseArray resolves to an array `a`, `filter`
+ * returns an array containing only those elements of `a` for which `fn` returns
+ * true.
+ * The resulting array can be used, e.g. in a template.
+ */
+
+/* Your task is to extend the DS.PromiseArray class with a similar function called
+ * `filterAsync`, which should have the same effect as `filter` with one subtle
+ * difference:
+ * The function `asyncFn`, which `filterAsync` takes as a parameter, takes
+ * a value, but instead of a Boolean, it returns a Promise which resolves to a
+ * Boolean.
+ * E.g. the function `isEvenAsync` above is such a function.
+ * `filterAsync` should still produce an array once the PromiseArray's underlying
+ * promise resolves.
+ */
+
+DS.PromiseArray.reopen({
+
+  /**
+   * @method filterAsync
+   * @param {Function<any -> Promise<Boolean>>} asyncFilterFn
+   * @return {Array}
+   */
+  filterAsync(asyncFn) {
+    return [42];
+  }
+});
+
+/* filteredModel and asyncFilteredModel below should eventually have the same value.
+ */
+export default Ember.Controller.extend({
+
+  _initModel: Ember.on('init', function() {
+    this.set('model', DS.PromiseArray.create({
+      promise: new Ember.RSVP.resolve([0,1,2,3,4,5,6,7,8])
+    }));
+  }),
+
+  filteredModel: Ember.computed('model.[]', function(){
+    return this.get('model').filter(isEven);
+  }),
+
+  asyncFilteredModel: Ember.computed('model.[]', function(){
+    return this.get('model').filterAsync(isEvenAsync);
+  }),
+
+});
diff --git a/templates.application.hbs b/templates.application.hbs
@@ -0,0 +1,7 @@
+{{#each filteredModel as |n|}}
+{{n}}
+{{/each}}
+<br>
+{{#each asyncFilteredModel as |n|}}
+{{n}}
+{{/each}}
diff --git a/twiddle.json b/twiddle.json
@@ -0,0 +1,17 @@
+{
+  "version": "0.10.1",
+  "EmberENV": {
+    "FEATURES": {}
+  },
+  "options": {
+    "use_pods": false,
+    "enable-testing": false
+  },
+  "dependencies": {
+    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
+    "ember": "2.6.0",
+    "ember-data": "2.6.1",
+    "ember-template-compiler": "2.6.0"
+  },
+  "addons": {}
+}
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