Array.every recipe

Author: joefiorini

chapters/arrays/testing-every-element.md

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+---
+layout: recipe
+title: Testing Every Element
+chapter: Arrays
+---
+## Problem
+
+You want to be able to check that every element in an array meets a particular condition.
+
+## Solution
+
+Use Array.every (ECMAScript 5):
+
+{% highlight coffeescript %}
+evens = (x for x in [1..10] by 2)
+
+evens.every (x)-> x % 2 == 0
+# => true
+{% endhighlight %}
+
+Array.every was addded to Mozilla's Javascript 1.6 and made standard with EcmaScript 5. If you to support browsers that do not implement EC5 then check out [`_.all` from underscore.js][underscore].
+
+For a real world example, prentend you have a multiple select list that looks like:
+
+{% highlight html %}
+<select multiple id="my-select-list">
+  <option>1</option>
+  <option>2</option>
+  <option>Red Car</option>
+  <option>Blue Car</option>
+</select>
+{% endhighlight %}
+
+Now you want to verify that the user selected only numbers. Let's use Array.every:
+
+{% highlight coffeescript %}
+validateNumeric = (item)->
+  parseFloat(item) == parseInt(item) && !isNaN(item)
+
+values = $("#my-select-list").val()
+
+values.every validateNumeric
+{% endhighlight %}
+
+## Discussion
+
+This is similar to using ruby's Array#all? method.
+
+[underscore]: http://documentcloud.github.com/underscore/