---
title: String.prototype.padStart()
slug: Web/JavaScript/Reference/Global_Objects/String/padStart
translation_of: Web/JavaScript/Reference/Global_Objects/String/padStart
---
<div>{{JSRef}}{{SeeCompatTable}}</div>

<p><strong><code>padStart()</code></strong><code> 會將用給定用於填充的字串，以重複的方式，插入到目標字串的起頭(左側)，直到目標字串到達指定長度。</code></p>

<h2 id="Syntax">Syntax</h2>

<pre class="syntaxbox"><var>str</var>.padStart(<var>targetLength</var> [, <var>padString</var>])</pre>

<h3 id="Parameters">Parameters</h3>

<dl>
 <dt><code>targetLength</code></dt>
 <dd>目標字串被填充後的長度。如果此參數小於原字串的長度，那將直接返回原字串。</dd>
 <dt><code>padString</code> {{optional_inline}}</dt>
 <dd>用來填充的字串。如果填充字串太長，則由左側開始，擷取所需要的長度。此參數預設值是空白 " " (U+0020).</dd>
</dl>

<h3 id="Return_value">Return value</h3>

<p>目標字串被填充到指定長度後，所得的新字串。</p>

<h2 id="Examples">Examples</h2>

<pre class="brush: js">'abc'.padStart(10);         // "       abc"
'abc'.padStart(10, "foo");  // "foofoofabc"
'abc'.padStart(6,"123465"); // "123abc"
</pre>

<h2 id="規範">規範</h2>

{{Specifications}}

<h2 id="瀏覽器相容性">瀏覽器相容性</h2>

{{Compat}}

<h2 id="See_also">See also</h2>

<ul>
 <li>{{jsxref("String.padEnd()")}}</li>
</ul>