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Revision 371157 of for each...in

  • Revision slug: JavaScript/Reference/Statements/for_each...in
  • Revision title: for each...in
  • Revision id: 371157
  • Created:
  • Creator: evilpie
  • Is current revision? No
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Revision Content

{{deprecated_header()}}

Summary

Iterates a specified variable over all values of object's properties. For each distinct property, a specified statement is executed.

The for each...in statement is deprecated as the part of ECMA-357 (E4X) standard. E4X will be disabled by default and removed in the future, but for each...in will not be disabled and removed because of backward compatibility considerations. Consider using for...of instead. (Please refer to {{ bug("791343")}}.)

for each...in is part of the ECMA-357 (E4X) standard, which is not widely supported by non-Mozilla browsers, not part of the ECMAScript standard.

Version Information

Statement
Implemented in: JavaScript 1.6
ECMAScript Version: none

Syntax

for each (variable in object) {
  statement
}

Parameters

variable
Variable to iterate over property values, optionally declared with the var keyword. This variable is local to the function, not to the loop.
object
Object for which the properties are iterated.
statement
A statement to execute for each property. To execute multiple statements within the loop, use a block statement ({ ... }) to group those statements.

Description

Some built-in properties are not iterated over. These include all built-in methods of objects, e.g. String's indexOf method. However, all user-defined properties are iterated over.

Examples

Example: Using for each...in

Warning: Never use a loop like this on arrays. Only use it on objects. Details.

The following snippet iterates over an object's properties, calculating their sum:

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

See also

  • for...in - a similar statement that iterates over the property names.
  • for...of - a similar statement that iterates over the property values. But there are some behavior that is different from for each...in statement.
  • for
  • Array comprehensions (these use for each)

Revision Source

<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 will be disabled by default and removed in the future, 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 class="note">
    <code>for each...in</code> is part of the <a class="external" href="http://www.ecma-international.org/publications/standards/Ecma-357.htm" title="http://www.ecma-international.org/publications/standards/Ecma-357.htm">ECMA-357 (E4X) standard</a>, which is not widely supported by non-Mozilla browsers, not part of the ECMAScript standard.</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 are some behavior that is different from <code>for each...in</code> statement.</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_Object">Array comprehensions</a> (these use <code>for each</code>)</li>
</ul>
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