Revision 651691 of function expression

  • リビジョンの URL スラグ: Web/JavaScript/Reference/Operators/function
  • リビジョンのタイトル: function expression
  • リビジョンの ID: 651691
  • 作成日:
  • 作成者: fscholz
  • 現行リビジョン いいえ
  • コメント

このリビジョンの内容

{{JSOperatorsQLAlpha()}}

Summary

The function keyword can be used to define a function inside an expression.

Syntax

function [name]([param1[, param2[, ..., paramN]]]) {
   statements
}

Parameters

name
The function name. Can be omitted, in which case the function is anonymous. The name is only local to the function body.
paramN
The name of an argument to be passed to the function. A function can have up to 255 arguments.
statements
The statements which comprise the body of the function.

Description

A function expression is very similar to and has almost the same syntax as a function statement (see function statement for details). The main difference between a function expression and a function statement is the function name, which can be omitted in function expressions to create anonymous functions. See also functions and function scope for more information.

Examples

The following example defines an unnamed function and assigns it to x. The function returns the square of its argument:

var x = function(y) {
   return y * y;
};

Named function expression

If you want to refer to the current function inside the function body, you need to create a named function expression. This name is then local only to the function body (scope). This also avoids using the non-standard arguments.callee property.

var math = {
  'factorial': function factorial(n) {
    if (n <= 1)
      return 1;
    return n * factorial(n - 1);
  }
};

Specifications

Specification Status Comment
ECMAScript 3rd Edition. Standard Initial definition. Implemented in JavaScript 1.5
{{SpecName('ES5.1', '#sec-13', 'Function definition')}} {{Spec2('ES5.1')}}  
{{SpecName('ES6', '#sec-function-definitions', 'Function definitions')}} {{Spec2('ES6')}}  

Browser compatibility

{{ CompatibilityTable() }}

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support {{ CompatVersionUnknown() }} {{ CompatVersionUnknown() }} {{ CompatVersionUnknown() }} {{ CompatVersionUnknown() }} {{ CompatVersionUnknown() }}
Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support {{ CompatVersionUnknown() }} {{ CompatVersionUnknown() }} {{ CompatVersionUnknown() }} {{ CompatVersionUnknown() }} {{ CompatVersionUnknown() }} {{ CompatVersionUnknown() }}

See also

このリビジョンのソースコード

<div>
 {{JSOperatorsQLAlpha()}}</div>
<h2 id="Summary">Summary</h2>
<p>The <code>function</code> keyword can be used to define a function inside an expression.</p>
<h2 id="Syntax" name="Syntax">Syntax</h2>
<pre class="syntaxbox">
function [<em>name</em>]([<em>param1</em>[, <em>param2[</em>, ..., <em>paramN</em>]]]) {
   <em>statements</em>
}</pre>
<h3 id="Parameters" name="Parameters">Parameters</h3>
<dl>
 <dt>
  <code>name</code></dt>
 <dd>
  The function name. Can be omitted, in which case the function is <em>anonymous</em>. The name is only local to the function body.</dd>
 <dt>
  <code>paramN</code></dt>
 <dd>
  The name of an argument to be passed to the function. A function can have up to 255 arguments.</dd>
 <dt>
  <code>statements</code></dt>
 <dd>
  The statements which comprise the body of the function.</dd>
</dl>
<h2 id="Description" name="Description">Description</h2>
<p>A function expression is very similar to and has almost the same syntax as a function statement (see <a href="/en-US/docs/Web/JavaScript/Reference/Statements/function">function statement</a> for details). The main difference between a function expression and a function statement is the <em>function name,</em> which can be omitted in function expressions to create <em>anonymous</em> functions. See also <a href="/en-US/docs/Web/JavaScript/Reference/Functions_and_function_scope">functions and function scope</a> for more information.</p>
<h2 id="Examples" name="Examples">Examples</h2>
<p>The following example defines an unnamed function and assigns it to <code>x</code>. The function returns the square of its argument:</p>
<pre class="brush: js">
var x = function(y) {
   return y * y;
};
</pre>
<h3 id="Named_function_expression">Named function expression</h3>
<p>If you want to refer to the current function inside the function body, you need to create a named function expression. This name is then local only to the function body (scope). This also avoids using the non-standard <a href="/en-US/docs/Web/JavaScript/Reference/Functions_and_function_scope/arguments/callee">arguments.callee</a> property.</p>
<pre class="brush: js">
var math = {
  'factorial': function factorial(n) {
    if (n &lt;= 1)
      return 1;
    return n * factorial(n - 1);
  }
};
</pre>
<h2 id="Specifications">Specifications</h2>
<table class="standard-table">
 <tbody>
  <tr>
   <th scope="col">Specification</th>
   <th scope="col">Status</th>
   <th scope="col">Comment</th>
  </tr>
  <tr>
   <td>ECMAScript 3rd Edition.</td>
   <td>Standard</td>
   <td>Initial definition. Implemented in JavaScript 1.5</td>
  </tr>
  <tr>
   <td>{{SpecName('ES5.1', '#sec-13', 'Function definition')}}</td>
   <td>{{Spec2('ES5.1')}}</td>
   <td>&nbsp;</td>
  </tr>
  <tr>
   <td>{{SpecName('ES6', '#sec-function-definitions', 'Function definitions')}}</td>
   <td>{{Spec2('ES6')}}</td>
   <td>&nbsp;</td>
  </tr>
 </tbody>
</table>
<h2 id="Browser_compatibility">Browser compatibility</h2>
<p>{{ CompatibilityTable() }}</p>
<div id="compat-desktop">
 <table class="compat-table">
  <tbody>
   <tr>
    <th>Feature</th>
    <th>Chrome</th>
    <th>Firefox (Gecko)</th>
    <th>Internet Explorer</th>
    <th>Opera</th>
    <th>Safari</th>
   </tr>
   <tr>
    <td>Basic support</td>
    <td>{{ CompatVersionUnknown() }}</td>
    <td>{{ CompatVersionUnknown() }}</td>
    <td>{{ CompatVersionUnknown() }}</td>
    <td>{{ CompatVersionUnknown() }}</td>
    <td>{{ CompatVersionUnknown() }}</td>
   </tr>
  </tbody>
 </table>
</div>
<div id="compat-mobile">
 <table class="compat-table">
  <tbody>
   <tr>
    <th>Feature</th>
    <th>Android</th>
    <th>Chrome for Android</th>
    <th>Firefox Mobile (Gecko)</th>
    <th>IE Mobile</th>
    <th>Opera Mobile</th>
    <th>Safari Mobile</th>
   </tr>
   <tr>
    <td>Basic support</td>
    <td>{{ CompatVersionUnknown() }}</td>
    <td>{{ CompatVersionUnknown() }}</td>
    <td>{{ CompatVersionUnknown() }}</td>
    <td>{{ CompatVersionUnknown() }}</td>
    <td>{{ CompatVersionUnknown() }}</td>
    <td>{{ CompatVersionUnknown() }}</td>
   </tr>
  </tbody>
 </table>
</div>
<h2 id="See_also" name="See_also">See also</h2>
<ul>
 <li><a href="/en-US/docs/Web/JavaScript/Reference/Functions_and_function_scope" title="JavaScript/Reference/Functions_and_function_scope">Functions and function scope</a></li>
 <li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" title="JavaScript/Reference/Global_Objects/Function"><code>Function</code></a></li>
 <li><a href="/en-US/docs/Web/JavaScript/Reference/Statements/function" title="JavaScript/Reference/Statements/function"><code>function statement</code></a></li>
</ul>
このリビジョンへ戻す