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+---
+title: Math.floor()
+slug: Web/JavaScript/Reference/Global_Objects/Math/floor
+tags:
+  - Math.floor()
+  - 向下取整
+translation_of: Web/JavaScript/Reference/Global_Objects/Math/floor
+---
+<div>{{JSRef}}<br>
+ </div>
+
+<p><code><strong>Math.floor()</strong></code> 返回小于或等于一个给定数字的最大整数。</p>
+
+<div class="note">
+<p>Note:  可以理解 <code><strong>Math.floor()</strong></code>为向下取整</p>
+</div>
+
+<h2 id="Syntax" name="Syntax">语法</h2>
+
+<pre class="syntaxbox notranslate"><code>Math.floor(<em>x</em>) </code></pre>
+
+<h3 id="Parameters" name="Parameters">参数</h3>
+
+<dl>
+ <dt><code>x</code></dt>
+ <dd>一个数字。</dd>
+ <dt>
+ <h3 id="返回值">返回值 </h3>
+
+ <p>一个表示小于或等于指定数字的最大整数的数字。</p>
+ </dt>
+</dl>
+
+<h2 id="Description" name="Description">描述</h2>
+
+<p>由于 <code>floor</code> 是 <code>Math</code> 的一个静态方法，你总是应该像这样使用它 <code>Math.floor()</code>，而不是作为你创建的一个Math对象的一种方法（Math不是一个构造函数）。</p>
+
+<h2 id="Examples" name="Examples">示例</h2>
+
+<h3 id="Example_Using_Math.floor" name="Example:_Using_Math.floor">例子：使用 <code>Math.floor</code></h3>
+
+<pre class="brush:js notranslate">Math.floor( 45.95);
+// 45
+Math.floor( 45.05);
+// 45
+Math.floor( 4 );
+// 4
+Math.floor(-45.05);
+// -46
+Math.floor(-45.95);
+// -46
+
+</pre>
+
+<h3 id="Example_Decimal_adjustment" name="Example:_Decimal_adjustment">例子：十进制调整</h3>
+
+<pre class="brush:js notranslate">// Closure
+(function(){
+
+	/**
+	 * Decimal adjustment of a number.
+	 *
+	 * @param	{String}	type	The type of adjustment.
+	 * @param	{Number}	value	The number.
+	 * @param	{Integer}	exp		The exponent (the 10 logarithm of the adjustment base).
+	 * @returns	{Number}			The adjusted value.
+	 */
+	function decimalAdjust(type, value, exp) {
+		// If the exp is undefined or zero...
+		if (typeof exp === 'undefined' || +exp === 0) {
+			return Math[type](value);
+		}
+		value = +value;
+		exp = +exp;
+		// If the value is not a number or the exp is not an integer...
+		if (isNaN(value) || !(typeof exp === 'number' &amp;&amp; exp % 1 === 0)) {
+			return NaN;
+		}
+		// Shift
+		value = value.toString().split('e');
+		value = Math[type](+(value[0] + 'e' + (value[1] ? (+value[1] - exp) : -exp)));
+		// Shift back
+		value = value.toString().split('e');
+		return +(value[0] + 'e' + (value[1] ? (+value[1] + exp) : exp));
+	}
+
+	// Decimal round
+	if (!Math.round10) {
+		Math.round10 = function(value, exp) {
+			return decimalAdjust('round', value, exp);
+		};
+	}
+	// Decimal floor
+	if (!Math.floor10) {
+		Math.floor10 = function(value, exp) {
+			return decimalAdjust('floor', value, exp);
+		};
+	}
+	// Decimal ceil
+	if (!Math.ceil10) {
+		Math.ceil10 = function(value, exp) {
+			return decimalAdjust('ceil', value, exp);
+		};
+	}
+
+})();
+
+// Round
+Math.round10(55.55, -1); // 55.6
+Math.round10(55.549, -1); // 55.5
+Math.round10(55, 1); // 60
+Math.round10(54.9, 1); // 50
+Math.round10(-55.55, -1); // -55.5
+Math.round10(-55.551, -1); // -55.6
+Math.round10(-55, 1); // -50
+Math.round10(-55.1, 1); // -60
+// Floor
+Math.floor10(55.59, -1); // 55.5
+Math.floor10(59, 1); // 50
+Math.floor10(-55.51, -1); // -55.6
+Math.floor10(-51, 1); // -60
+// Ceil
+Math.ceil10(55.51, -1); // 55.6
+Math.ceil10(51, 1); // 60
+Math.ceil10(-55.59, -1); // -55.5
+Math.ceil10(-59, 1); // -50
+</pre>
+
+<h2 id="规范">规范</h2>
+
+<table class="standard-table">
+ <tbody>
+  <tr>
+   <th scope="col">规范版本</th>
+   <th scope="col">规范状态</th>
+   <th scope="col">注解</th>
+  </tr>
+  <tr>
+   <td>ECMAScript 1st Edition. Implemented in JavaScript 1.0</td>
+   <td>Standard</td>
+   <td>Initial definition.</td>
+  </tr>
+  <tr>
+   <td>{{SpecName('ES5.1', '#sec-15.8.2.9', 'Math.floor')}}</td>
+   <td>{{Spec2('ES5.1')}}</td>
+   <td></td>
+  </tr>
+  <tr>
+   <td>{{SpecName('ES6', '#sec-math.floor', 'Math.floor')}}<span style="display: none;"> </span></td>
+   <td>{{Spec2('ES6')}}</td>
+   <td></td>
+  </tr>
+  <tr>
+   <td>{{SpecName('ESDraft', '#sec-math.floor', 'Math.floor')}}</td>
+   <td>{{Spec2('ESDraft')}}</td>
+   <td></td>
+  </tr>
+ </tbody>
+</table>
+
+<h2 id="浏览器兼容性">浏览器兼容性</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">相关链接</h2>
+
+<ul>
+ <li>The {{jsxref("Global_Objects/Math", "Math")}} object it belongs to.</li>
+ <li>{{jsxref("Math.abs")}}</li>
+ <li>{{jsxref("Math.ceil()")}}</li>
+ <li>{{jsxref("Math.round()")}}</li>
+ <li>{{jsxref("Math.sign()")}}</li>
+ <li>{{jsxref("Math.trunc()")}}</li>
+</ul>