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---
title: Math.floor()
slug: Web/JavaScript/Reference/Global_Objects/Math/floor
tags:
- JavaScript
- Math
- Method
- Reference
translation_of: Web/JavaScript/Reference/Global_Objects/Math/floor
---
<div>{{JSRef}}</div>
<p><strong><code>Math.floor()</code></strong> 函式會回傳小於等於所給數字的最大整數。</p>
<div>{{EmbedInteractiveExample("pages/js/math-floor.html")}}</div>
<h2 id="語法">語法</h2>
<pre class="syntaxbox"><code>Math.floor(<var>x</var>)</code></pre>
<h3 id="參數">參數</h3>
<dl>
<dt><code>x</code></dt>
<dd>數字型態。</dd>
</dl>
<h3 id="回傳值">回傳值</h3>
<p>小於等於所給數字的最大整數。</p>
<h2 id="描述">描述</h2>
<p> <code>floor()</code> 是 <code>Math</code>的靜態函式, 所以不需實體化<code>Math</code> 物件, 只要直接呼叫 <code>Math.floor()</code>就能使用。</p>
<p>(此外<code>Math</code> 並不是建構子).</p>
<h2 id="範例">範例</h2>
<h3 id="使用_Math.floor">使用 <code>Math.floor()</code></h3>
<pre class="brush: js">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="Decimal_adjustment">Decimal adjustment</h3>
<pre class="brush: js">// 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' && 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="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 1.0.</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')}}</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="瀏覽器相容性">瀏覽器相容性</h2>
<p>{{Compat("javascript.builtins.Math.floor")}}</p>
<h2 id="參見">參見</h2>
<ul>
<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>
|
