path: root/files/zh-tw/web/javascript/reference/functions/arguments/index.html

---
title: Arguments 物件
slug: Web/JavaScript/Reference/Functions/arguments
tags:
  - Functions
  - JavaScript
  - Reference
  - arguments
translation_of: Web/JavaScript/Reference/Functions/arguments
---
<div>
<div>{{jsSidebar("Functions")}}</div>
</div>

<p><strong><code>arguments</code></strong> 物件是一個對應傳入函式之引數的類陣列（<code>Array-like</code>）物件。</p>

<h2 id="語法">語法</h2>

<pre class="syntaxbox">arguments</pre>

<h2 id="描述">描述</h2>

<div class="blockIndicator note">
<p>Note: 如果你有在使用 ES6 語法，建議參考<a href="https://developer.mozilla.org/zh-TW/docs/Web/JavaScript/Reference/Functions/rest_parameters">其餘參數</a>。</p>
</div>

<div class="blockIndicator note">
<p>Note: 「類陣列 (Array-like)」 的意思是 <code>arguments</code> 一樣擁有 <code>length</code>這項屬性，以及從 0 開始的索引，但是它沒有陣列內建的方法像是 <code>forEach()</code> ，或是 <code>map()</code> 。</p>
</div>

<p>The <code>arguments</code> object is a local variable available within all (non-arrow) functions. You can refer to a function's arguments within the function by using the <code>arguments</code> object. This object contains an entry for each argument passed to the function, the first entry's index starting at 0.</p>

<p>For example, if a function is passed three arguments, you can refer to them as follows:</p>

<pre class="brush: js">arguments[0]
arguments[1]
arguments[2]
</pre>

<p>arguments 也可以被指定：</p>

<pre class="brush: js">arguments[1] = 'new value';</pre>

<p><code>arguments</code> 物件不是陣列。它與陣列非常相似，但是它沒有除了 <code>length</code> 這個屬性以外的其他陣列屬性。舉例，它沒有 <code>pop</code> 這個陣列方法。</p>

<p>然而，它依然可以被轉換為真正的陣列(Array)。</p>

<pre class="brush: js">var args = Array.prototype.slice.call(arguments);
var args = [].slice.call(arguments);

// ES2015
const args = Array.from(arguments);
</pre>

<div class="warning">
<p class="brush: js">Using slice on arguments prevents optimizations in some JavaScript engines (V8 for example - <a href="https://github.com/petkaantonov/bluebird/wiki/Optimization-killers#3-managing-arguments">more information</a>). If you care for them, try constructing a new array by iterating through the arguments object instead. An alternative would be to use the despised <code>Array</code> constructor as a function:</p>

<pre class="brush: js">var args = (arguments.length === 1 ? [arguments[0]] : Array.apply(null, arguments));</pre>
</div>

<p>You can use the <code>arguments</code> object if you call a function with more arguments than it is formally declared to accept. This technique is useful for functions that can be passed a variable number of arguments. Use <code><a href="/en-US/docs/JavaScript/Reference/Functions_and_function_scope/arguments/length">arguments.length</a></code> to determine the number of arguments passed to the function, and then process each argument by using the <code>arguments</code> object. To determine the number of parameters in the function <a href="/en-US/docs/Glossary/Signature/Function">signature</a>, use the <code><a href="/en-US/docs/JavaScript/Reference/Global_Objects/Function/length">Function.length</a></code> property.</p>

<h3 id="Using_typeof_with_Arguments">Using <code>typeof</code> with Arguments</h3>

<p>The typeof arguments returns 'object'. </p>

<pre>console.log(typeof arguments); // 'object' </pre>

<p>The typeof individual arguments can be determined with the use of indexing.</p>

<pre>console.log(typeof arguments[0]); //this will return the typeof individual arguments.</pre>

<h3 id="Using_the_Spread_Syntax_with_Arguments">Using the Spread Syntax with Arguments</h3>

<p>You can also use the {{jsxref("Array.from()")}} method or the <a href="/en-US/docs/Web/JavaScript/Reference/Operators/Spread_operator">spread operator</a> to convert arguments to a real Array:</p>

<pre class="brush: js">var args = Array.from(arguments);
var args = [...arguments];
</pre>

<h2 id="屬性">屬性</h2>

<dl>
 <dt><code><a href="/en-US/docs/Web/JavaScript/Reference/Functions/arguments/callee">arguments.callee</a></code></dt>
 <dd>Reference to the currently executing function.</dd>
 <dt><code><a href="/en-US/docs/Web/JavaScript/Reference/Functions/arguments/caller">arguments.caller</a></code> {{ Obsolete_inline() }}</dt>
 <dd>Reference to the function that invoked the currently executing function.</dd>
 <dt><code><a href="/en-US/docs/Web/JavaScript/Reference/Functions/arguments/length">arguments.length</a></code></dt>
 <dd>Reference to the number of arguments passed to the function.</dd>
 <dt><code><a href="/en-US/docs/Web/JavaScript/Reference/Functions/arguments/@@iterator">arguments[@@iterator]</a></code></dt>
 <dd>Returns a new Array Iterator object that contains the values for each index in the arguments.</dd>
</dl>

<h2 id="範例">範例</h2>

<h3 id="Defining_a_function_that_concatenates_several_strings">Defining a function that concatenates several strings</h3>

<p>This example defines a function that concatenates several strings. The only formal argument for the function is a string that specifies the characters that separate the items to concatenate. The function is defined as follows:</p>

<pre class="brush:js">function myConcat(separator) {
  var args = Array.prototype.slice.call(arguments, 1);
  return args.join(separator);
}</pre>

<p>You can pass any number of arguments to this function, and it creates a list using each argument as an item in the list.</p>

<pre class="brush:js">// returns "red, orange, blue"
myConcat(', ', 'red', 'orange', 'blue');

// returns "elephant; giraffe; lion; cheetah"
myConcat('; ', 'elephant', 'giraffe', 'lion', 'cheetah');

// returns "sage. basil. oregano. pepper. parsley"
myConcat('. ', 'sage', 'basil', 'oregano', 'pepper', 'parsley');</pre>

<h3 id="Defining_a_function_that_creates_HTML_lists">Defining a function that creates HTML lists</h3>

<p>This example defines a function that creates a string containing HTML for a list. The only formal argument for the function is a string that is "<code>u</code>" if the list is to be unordered (bulleted), or "<code>o</code>" if the list is to be ordered (numbered). The function is defined as follows:</p>

<pre class="brush:js">function list(type) {
  var result = '&lt;' + type + 'l&gt;&lt;li&gt;';
  var args = Array.prototype.slice.call(arguments, 1);
  result += args.join('&lt;/li&gt;&lt;li&gt;');
  result += '&lt;/li&gt;&lt;/' + type + 'l&gt;'; // end list

  return result;
}</pre>

<p>You can pass any number of arguments to this function, and it adds each argument as an item to a list of the type indicated. For example:</p>

<pre class="brush:js">var listHTML = list('u', 'One', 'Two', 'Three');

/* listHTML is:

"&lt;ul&gt;&lt;li&gt;One&lt;/li&gt;&lt;li&gt;Two&lt;/li&gt;&lt;li&gt;Three&lt;/li&gt;&lt;/ul&gt;"

*/</pre>

<h3 id="Rest_default_and_destructured_parameters">Rest, default, and destructured parameters</h3>

<p>The <code>arguments</code> object can be used in conjunction with <a href="/en-US/docs/Web/JavaScript/Reference/Functions/rest_parameters">rest</a>, <a href="/en-US/docs/Web/JavaScript/Reference/Functions/Default_parameters">default</a>, and <a href="/en-US/docs/Web/JavaScript/Reference/Operators/Destructuring_assignment">destructured</a> parameters.</p>

<pre class="brush: js">function foo(...args) {
  return args;
}
foo(1, 2, 3); // [1,2,3]
</pre>

<p>While the presence of <a href="/en-US/docs/Web/JavaScript/Reference/Functions/rest_parameters">rest</a>, <a href="/en-US/docs/Web/JavaScript/Reference/Functions/Default_parameters">default</a>, or <a href="/en-US/docs/Web/JavaScript/Reference/Operators/Destructuring_assignment">destructured</a> parameters does not alter the <a href="/en-US/docs/Web/JavaScript/Reference/Strict_mode#Making_eval_and_arguments_simpler">behavior of the <code>arguments</code> object in strict mode code</a>, there is a subtle difference for non-strict code.</p>

<p>When a non-strict function <strong><strong>does </strong>not</strong> contain <a href="/en-US/docs/Web/JavaScript/Reference/Functions/rest_parameters">rest</a>, <a href="/en-US/docs/Web/JavaScript/Reference/Functions/Default_parameters">default</a>, or <a href="/en-US/docs/Web/JavaScript/Reference/Operators/Destructuring_assignment">destructured</a> parameters, then the values in the <code>arguments</code> object <strong>do</strong> track the values of the arguments (and vice versa). See the code below:</p>

<pre class="brush: js">function func(a) {
  arguments[0] = 99; // updating arguments[0] also updates a
  console.log(a);
}
func(10); // 99
</pre>

<p>and</p>

<pre class="brush: js">function func(a) {
  a = 99; // updating a also updates arguments[0]
  console.log(arguments[0]);
}
func(10); // 99
</pre>

<p>When a non-strict function <strong>does</strong> contain <a href="/en-US/docs/Web/JavaScript/Reference/Functions/rest_parameters">rest</a>, <a href="/en-US/docs/Web/JavaScript/Reference/Functions/Default_parameters">default</a>, or <a href="/en-US/docs/Web/JavaScript/Reference/Operators/Destructuring_assignment">destructured</a> parameters, then the values in the <code>arguments</code> object <strong>do not</strong> track the values of the arguments (and vice versa). Instead, they reflect the arguments provided at the time of invocation:</p>

<pre class="brush: js">function func(a = 55) {
  arguments[0] = 99; // updating arguments[0] does not also update a
  console.log(a);
}
func(10); // 10</pre>

<p>and</p>

<pre class="brush: js">function func(a = 55) {
  a = 99; // updating a does not also update arguments[0]
  console.log(arguments[0]);
}
func(10); // 10
</pre>

<p>and</p>

<pre class="brush: js">function func(a = 55) {
  console.log(arguments[0]);
}
func(); // undefined</pre>

<h2 id="規範">規範</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>{{SpecName('ES1')}}</td>
   <td>{{Spec2('ES1')}}</td>
   <td>Initial definition. Implemented in JavaScript 1.1</td>
  </tr>
  <tr>
   <td>{{SpecName('ES5.1', '#sec-10.6', 'Arguments Object')}}</td>
   <td>{{Spec2('ES5.1')}}</td>
   <td></td>
  </tr>
  <tr>
   <td>{{SpecName('ES2015', '#sec-arguments-exotic-objects', 'Arguments Exotic Objects')}}</td>
   <td>{{Spec2('ES2015')}}</td>
   <td></td>
  </tr>
  <tr>
   <td>{{SpecName('ESDraft', '#sec-arguments-exotic-objects', 'Arguments Exotic Objects')}}</td>
   <td>{{Spec2('ESDraft')}}</td>
   <td></td>
  </tr>
 </tbody>
</table>

<h2 id="瀏覽器相容性">瀏覽器相容性</h2>



<p>{{Compat("javascript.functions.arguments")}}</p>

<h2 id="參見">參見</h2>

<ul>
 <li>{{jsxref("Function")}}</li>
</ul>