--- title: Math.abs() slug: Web/JavaScript/Reference/Global_Objects/Math/abs tags: - JavaScript - Math - Method - Reference translation_of: Web/JavaScript/Reference/Global_Objects/Math/abs ---
{{JSRef}}

Math.abs() 函式會回傳一個數字的絕對值，即為：

Math.abs(x)=|x|={xifx>00ifx=0-xifx<0{\mathtt{\operatorname{Math.abs}(x)}} = {|x|} = \begin{cases} x & \text{if} \quad x \geq 0 \\ x & \text{if} \quad x < 0 \end{cases}

{{EmbedInteractiveExample("pages/js/math-abs.html")}}

語法

Math.abs(x)

參數

x
一個數字。

回傳值

給定數字的絕對值。

描述

Because abs() is a static method of Math, you always use it as Math.abs(), rather than as a method of a Math object you created (Math is not a constructor).

範例

Math.abs() 的行為

Passing an empty object, an array with more than one member, a non-numeric string or {{jsxref("undefined")}}/empty variable returns {{jsxref("NaN")}}. Passing {{jsxref("null")}}, an empty string or an empty array returns 0.

Math.abs('-1');     // 1
Math.abs(-2);       // 2
Math.abs(null);     // 0
Math.abs('');       // 0
Math.abs([]);       // 0
Math.abs([2]);      // 2
Math.abs([1,2]);    // NaN
Math.abs({});       // NaN
Math.abs('string'); // NaN
Math.abs();         // NaN

規範

Specification Status Comment
{{SpecName('ES1')}} {{Spec2('ES1')}} Initial definition. Implemented in JavaScript 1.0.
{{SpecName('ES5.1', '#sec-15.8.2.1', 'Math.abs')}} {{Spec2('ES5.1')}}  
{{SpecName('ES6', '#sec-math.abs', 'Math.abs')}} {{Spec2('ES6')}}  
{{SpecName('ESDraft', '#sec-math.abs', 'Math.abs')}} {{Spec2('ESDraft')}}  

瀏覽器相容性

{{Compat("javascript.builtins.Math.abs")}}

參見