Revision 535339 of for each...in

<p>{{deprecated_header()}}</p>
<h2 id="Summary">Summary</h2>
<p>Iterates a specified variable over all values of object's properties. For each distinct property, a specified statement is executed.</p>
<div class="noinclude">
 <div class="warning">
  <p>The for each...in statement is deprecated as the part of ECMA-357 (<a href="/en-US/docs/E4X" title="/en-US/docs/E4X">E4X</a>) standard. E4X support has been removed, but for each...in will not be disabled and removed because of backward compatibility considerations. Consider using <a href="/en-US/docs/JavaScript/Reference/Statements/for...of" title="/en-US/docs/JavaScript/Reference/Statements/for...of">for...of</a> instead. (Please refer to {{ bug("791343")}}.)</p>
 </div>
</div>
<h2 id="Version_Information">Version Information</h2>
<table class="standard-table">
 <tbody>
  <tr>
   <td class="header" colspan="2">Statement</td>
  </tr>
  <tr>
   <td>Implemented in:</td>
   <td><a href="/en-US/docs/JavaScript/New_in_JavaScript/1.6" title="JavaScript/New_in_JavaScript/1.6">JavaScript 1.6</a></td>
  </tr>
  <tr>
   <td>ECMAScript Version:</td>
   <td>none</td>
  </tr>
 </tbody>
</table>
<h2 id="Syntax" name="Syntax">Syntax</h2>
<pre class="syntaxbox">
<code>for each (<em>variable</em> in <em>object</em>) {
  <em>statement</em>
}</code></pre>
<h2 id="Parameters" name="Parameters">Parameters</h2>
<dl>
 <dt>
  <code>variable</code></dt>
 <dd>
  Variable to iterate over property values, optionally declared with the <code>var</code> keyword. This variable is local to the function, not to the loop.</dd>
</dl>
<dl>
 <dt>
  <code>object</code></dt>
 <dd>
  Object for which the properties are iterated.</dd>
</dl>
<dl>
 <dt>
  <code>statement</code></dt>
 <dd>
  A statement to execute for each property. To execute multiple statements within the loop, use a <a href="/en-US/docs/JavaScript/Reference/Statements/block" title="JavaScript/Reference/Statements/block">block</a> statement (<code>{ ... }</code>) to group those statements.</dd>
</dl>
<h2 id="Description" name="Description">Description</h2>
<p>Some built-in properties are not iterated over. These include all built-in methods of objects, e.g. <code>String</code>'s <code>indexOf</code> method. However, all user-defined properties are iterated over.</p>
<h2 id="Examples" name="Examples">Examples</h2>
<h3 id="Example:_Using_for_each...in" name="Example:_Using_for_each...in">Example: Using <code>for each...in</code></h3>
<p><strong>Warning:</strong> Never use a loop like this on arrays. Only use it on objects. <a href="/en-US/docs/JavaScript/Reference/Statements/for...in#Description" title="JavaScript/Reference/Statements/for...in#Description">Details</a>.</p>
<p>The following snippet iterates over an object's properties, calculating their sum:</p>
<pre class="brush:js">
var sum = 0;
var obj = {prop1: 5, prop2: 13, prop3: 8};

for each (var item in obj) {
  sum += item;
}

print(sum); // prints "26", which is 5+13+8</pre>
<h2 id="See_also" name="See_also">See also</h2>
<ul>
 <li><a href="/en-US/docs/JavaScript/Reference/Statements/for...in" title="JavaScript/Reference/Statements/for...in">for...in</a> - a similar statement that iterates over the property <em>names</em>.</li>
 <li><a href="/en-US/docs/JavaScript/Reference/Statements/for...of" title="/en-US/docs/JavaScript/Reference/Statements/for...of">for...of</a> - a similar statement that iterates over the property <em>values</em> but there is some behavior that is different from <code>for each...in</code> statements.</li>
 <li><a href="/en-US/docs/JavaScript/Reference/Statements/for" title="JavaScript/Reference/Statements/for">for</a></li>
 <li><a href="/en-US/docs/JavaScript/Guide/Predefined_Core_Objects#Array_comprehensions">Array comprehensions</a> (these use <code>for each</code>)</li>
 <li><a href="/en-US/docs/Web/JavaScript/Guide/Iterators_and_Generators" title="/en-US/docs/Web/JavaScript/Guide/Iterators_and_Generators">Iterator</a> - a function that takes a collection as an argument and allows traversal of its properties through subsequent methods</li>
</ul>