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---
title: Console.assert()
slug: Web/API/console/assert
tags:
- API
- DOM
- Debugging
- 函式
- 控制台
- 網頁控制台
- 網頁開發
translation_of: Web/API/console/assert
---
<div>{{APIRef("Console API")}}</div>
<p>如果斷言（assertion）為非（false），主控台會顯示錯誤訊息；如果斷言為是（true），則不發生任何事。</p>
<p>{{AvailableInWorkers}}</p>
<div class="note">
<p><strong>注意</strong>：<em>在 Node.js 內 <code>console.assert()</code> 方法的實做，與瀏覽器並不相同。</em></p>
<p>瀏覽器內呼叫 falsy 的 <code>console.assert()</code> 斷言出現 <code>message</code>，但不會中斷程式碼的執行。然而在 Node.js 裡面，falsy 斷言會拋出 <code>AssertionError</code> 錯誤。</p>
</div>
<h2 id="語法">語法</h2>
<pre class="syntaxbox">console.assert(<em>assertion</em>, <em>obj1</em> [, <em>obj2</em>, ..., <em>objN</em>]);
console.assert(<em>assertion</em>, <em>msg</em> [, <em>subst1</em>, ..., <em>substN</em>]); // c-like message formatting
</pre>
<h3 id="參數">參數</h3>
<dl>
<dt><code>assertion</code></dt>
<dd>布林表達式。如果斷言為非，訊息會出現在主控台上。</dd>
<dt><code>obj1</code> ... <code>objN</code></dt>
<dd>要印出來的 JavaScript 物件名單。 The string representations of each of these objects are appended together in the order listed and output.</dd>
<dt><code>msg</code></dt>
<dd>包含零個以上的 JavaScript 替代（substitution）字串。</dd>
<dt><code>subst1</code> ... <code>substN</code></dt>
<dd>JavaScript objects with which to replace substitution strings within <code>msg</code>. This parameter gives you additional control over the format of the output.</dd>
</dl>
<p>請參見 {{domxref("console")}} 的 <a href="/zh-TW/docs/Web/API/console#Outputting_text_to_the_console">Outputting text to the console</a> 以獲取詳細資訊。</p>
<h2 id="範例">範例</h2>
<p>以下程式碼示範一個 JavaScript 物件的斷言使用：</p>
<pre class="brush: js">const errorMsg = 'the # is not even';
for (let number = 2; number <= 5; number += 1) {
console.log('the # is ' + number);
console.assert(number % 2 === 0, {number: number, errorMsg: errorMsg});
// or, using ES2015 object property shorthand:
// console.assert(number % 2 === 0, {number, errorMsg});
}
// output:
// the # is 2
// the # is 3
// Assertion failed: {number: 3, errorMsg: "the # is not even"}
// the # is 4
// the # is 5
// Assertion failed: {number: 5, errorMsg: "the # is not even"}
</pre>
<p>請注意，雖然包含替換字符串的字符串在 Node 中用作 <code>console.log</code> 的參數，但很多（如果不是大多數）瀏覽器...</p>
<pre class="brush: js">console.log('the word is %s', 'foo');
// output: the word is foo
</pre>
<p>...在所有瀏覽器中，使用此類字符串目前無法作為console.assert的參數使用：</p>
<pre class="brush: js">console.assert(false, 'the word is %s', 'foo');
// correct output in Node (e.g. v8.10.0) and some browsers
// (e.g. Firefox v60.0.2):
// Assertion failed: the word is foo
// incorrect output in some browsers
// (e.g. Chrome v67.0.3396.87):
// Assertion failed: the word is %s foo
</pre>
<p>有關詳細信息，請參閱 {{domxref("console")}} 文檔中的<a href="https://developer.mozilla.org/zh-TW/docs/Web/API/console#Outputting_text_to_the_console">將文本輸出到控制台</a>。</p>
<h2 id="規範">規範</h2>
<table class="standard-table">
<thead>
<tr>
<th scope="col">Specification</th>
<th scope="col">Status</th>
<th scope="col">Comment</th>
</tr>
</thead>
<tbody>
<tr>
<td>{{SpecName("Console API", "#assert", "console.assert()")}}</td>
<td>{{Spec2("Console API")}}</td>
<td>初始定義</td>
</tr>
</tbody>
</table>
<h2 id="瀏覽器相容性">瀏覽器相容性</h2>
<p>{{Compat("api.Console.assert")}}</p>
<h2 id="參見">參見</h2>
<ul>
<li><a href="https://console.spec.whatwg.org/#assert-condition-data">WHATWG Console Standard: console.assert</a></li>
<li><a href="http://www.opera.com/dragonfly/documentation/console/">Opera Dragonfly documentation: Console</a></li>
<li><a href="http://msdn.microsoft.com/library/gg589530">MSDN: Using the F12 Tools Console to View Errors and Status</a></li>
<li><a href="https://developer.chrome.com/devtools/docs/console#assertions">Chrome Developer Tools: Using the Console</a></li>
</ul>
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