path: root/files/zh-tw/conflicting/web/javascript/reference/operators/index.html

---
title: 算術運算子
slug: conflicting/Web/JavaScript/Reference/Operators
translation_of: Web/JavaScript/Reference/Operators
translation_of_original: Web/JavaScript/Reference/Operators/Arithmetic_Operators
original_slug: Web/JavaScript/Reference/Operators/Arithmetic_Operators
---
<div>{{jsSidebar("Operators")}}</div>

<p><strong>算術運算子接受數值（資料型態為字串或變數都可）作為其運算子並回傳單個數值。 標準算術運算符號有加號（+），減號（ - ），乘（*）和除（/）。</strong></p>

<div>{{EmbedInteractiveExample("pages/js/expressions-arithmetic.html")}}</div>



<h2 id="Addition_()"><a id="加法" name="加法">Addition (+)</a></h2>

<p>加法運算子生成數字(運算元)的總和或字串串接。</p>

<h3 id="Syntax">Syntax</h3>

<pre class="syntaxbox"><strong>Operator:</strong> x + y
</pre>

<h3 id="Examples">Examples</h3>

<pre class="brush: js">// Number + Number -&gt; addition
1 + 2 // 3

// Boolean + Number -&gt; addition
true + 1 // 2

// Boolean + Boolean -&gt; addition
false + false // 0

// Number + String -&gt; concatenation
5 + 'foo' // "5foo"

// String + Boolean -&gt; concatenation
'foo' + false // "foofalse"

// String + String -&gt; concatenation
'foo' + 'bar' // "foobar"
</pre>

<h2 id="Subtraction_(-)"><a id="減法" name="減法">Subtraction (-)</a></h2>

<p>減法運算子能算出兩個運算元間的差異。</p>

<h3 id="Syntax_2">Syntax</h3>

<pre class="syntaxbox"><strong>Operator:</strong> x - y
</pre>

<h3 id="Examples_2">Examples</h3>

<pre class="brush: js">5 - 3 // 2
3 - 5 // -2
'foo' - 3 // NaN</pre>

<h2 id="Division_()"><a id="除法" name="除法">Division (/)</a></h2>

<p>The division operator produces the quotient of its operands where the left operand is the dividend and the right operand is the divisor.</p>

<h3 id="Syntax_3">Syntax</h3>

<pre class="syntaxbox"><strong>Operator:</strong> x / y
</pre>

<h3 id="Examples_3">Examples</h3>

<pre class="brush: js">1 / 2      // returns 0.5 in JavaScript
1 / 2      // returns 0 in Java
// (neither number is explicitly a floating point number)

1.0 / 2.0  // returns 0.5 in both JavaScript and Java

2.0 / 0    // returns Infinity in JavaScript
2.0 / 0.0  // returns Infinity too
2.0 / -0.0 // returns -Infinity in JavaScript</pre>

<h2 id="Multiplication_(*)"><a id="乘法" name="乘法">Multiplication (*)</a></h2>

<p>The multiplication operator produces the product of the operands.</p>

<h3 id="Syntax_4">Syntax</h3>

<pre class="syntaxbox"><strong>Operator:</strong> x * y
</pre>

<h3 id="Examples_4">Examples</h3>

<pre class="brush: js">2 * 2 // 4
-2 * 2 // -4
Infinity * 0 // NaN
Infinity * Infinity // Infinity
'foo' * 2 // NaN
</pre>

<h2 id="Remainder_()"><a id="餘數運算" name="餘數運算">Remainder (%)</a></h2>

<p>The remainder operator returns the remainder left over when one operand is divided by a second operand. It always takes the sign of the dividend.</p>

<h3 id="Syntax_5">Syntax</h3>

<pre class="syntaxbox"><strong>Operator:</strong> var1 % var2
</pre>

<h3 id="Examples_5">Examples</h3>

<pre class="brush: js">12 % 5 // 2
-1 % 2 // -1
1 % -2 // 1
NaN % 2 // NaN
1 % 2 // 1
2 % 3 // 2
-4 % 2 // -0
5.5 % 2 // 1.5
</pre>

<h2 id="Exponentiation_(**)"><a id="指數運算" name="指數運算">Exponentiation (**)</a></h2>

<p>The exponentiation operator returns the result of raising first operand to the power second operand. that is, <code>var1</code><sup><code>var2</code></sup>, in the preceding statement, where <code>var1</code> and <code>var2</code> are variables. Exponentiation operator is right associative. <code>a ** b ** c</code> is equal to <code>a ** (b ** c)</code>.</p>

<h3 id="Syntax_6">Syntax</h3>

<pre class="syntaxbox"><strong>Operator:</strong> var1 ** var2
</pre>

<h3 id="Notes">Notes</h3>

<p>In most languages like PHP and Python and others that have an exponentiation operator (**), the exponentiation operator is defined to have a higher precedence than unary operators such as unary + and unary -, but there are a few exceptions. For example, in Bash the ** operator is defined to have a lower precedence than unary operators. In JavaScript, it is impossible to write an ambiguous exponentiation expression, i.e. you cannot put a unary operator (<code>+/-/~/!/delete/void/typeof</code>) immediately before the base number.</p>

<pre class="brush: js">-2 ** 2;
// 4 in Bash, -4 in other languages.
// This is invalid in JavaScript, as the operation is ambiguous.


-(2 ** 2);
// -4 in JavaScript and the author's intention is unambiguous.
</pre>

<h3 id="Examples_6">Examples</h3>

<pre class="brush: js">2 ** 3 // 8
3 ** 2 // 9
3 ** 2.5 // 15.588457268119896
10 ** -1 // 0.1
NaN ** 2 // NaN

2 ** 3 ** 2 // 512
2 ** (3 ** 2) // 512
(2 ** 3) ** 2 // 64
</pre>

<p>To invert the sign of the result of an exponentiation expression:</p>

<pre class="brush: js">-(2 ** 2) // -4
</pre>

<p>To force the base of an exponentiation expression to be a negative number:</p>

<pre class="brush: js">(-2) ** 2 // 4
</pre>

<div class="note">
<p><strong>Note:</strong> JavaScript also has <a href="/en-US/docs/Web/JavaScript/Reference/Operators/Bitwise_Operators#Bitwise_XOR">a bitwise operator ^ (logical XOR)</a>. <code>**</code> and <code>^</code> are different (for example : <code>2 ** 3 === 8</code> when <code>2 ^ 3 === 1</code>.)</p>
</div>

<h2 id="Increment_()"><a id="遞增運算" name="遞增運算">Increment (++)</a></h2>

<p>The increment operator increments (adds one to) its operand and returns a value.</p>

<ul>
 <li>If used postfix, with operator after operand (for example, x++), then it returns the value before incrementing.</li>
 <li>If used prefix with operator before operand (for example, ++x), then it returns the value after incrementing.</li>
</ul>

<h3 id="Syntax_7">Syntax</h3>

<pre class="syntaxbox"><strong>Operator:</strong> x++ or ++x
</pre>

<h3 id="Examples_7">Examples</h3>

<pre class="brush: js">// Postfix
var x = 3;
y = x++; // y = 3, x = 4

// Prefix
var a = 2;
b = ++a; // a = 3, b = 3
</pre>

<h2 id="Decrement_(--)"><a id="遞減運算" name="遞減運算">Decrement (--)</a></h2>

<p>The decrement operator decrements (subtracts one from) its operand and returns a value.</p>

<ul>
 <li>If used postfix (for example, x--), then it returns the value before decrementing.</li>
 <li>If used prefix (for example, --x), then it returns the value after decrementing.</li>
</ul>

<h3 id="Syntax_8">Syntax</h3>

<pre class="syntaxbox"><strong>Operator:</strong> x-- or --x
</pre>

<h3 id="Examples_8">Examples</h3>

<pre class="brush: js">// Postfix
var x = 3;
y = x--; // y = 3, x = 2

// Prefix
var a = 2;
b = --a; // a = 1, b = 1
</pre>

<h2 id="Unary_negation_(-)"><a name="Unary_negation">Unary negation (-)</a></h2>

<p>The unary negation operator precedes its operand and negates it.</p>

<h3 id="Syntax_9">Syntax</h3>

<pre class="syntaxbox"><strong>Operator:</strong> -x
</pre>

<h3 id="Examples_9">Examples</h3>

<pre class="brush: js">var x = 3;
y = -x; // y = -3, x = 3

// Unary negation operator can convert non-numbers into a number
var x = "4";
y = -x; // y = -4
</pre>

<h2 id="Unary_plus_()"><a name="Unary_plus">Unary plus</a> (+)</h2>

<p>The unary plus operator precedes its operand and evaluates to its operand but attempts to convert it into a number, if it isn't already. Although unary negation (-) also can convert non-numbers, unary plus is the fastest and preferred way of converting something into a number, because it does not perform any other operations on the number. It can convert string representations of integers and floats, as well as the non-string values <code>true</code>, <code>false</code>, and <code>null</code>. Integers in both decimal and hexadecimal ("0x"-prefixed) formats are supported. Negative numbers are supported (though not for hex). If it cannot parse a particular value, it will evaluate to {{jsxref("NaN")}}.</p>

<h3 id="Syntax_10">Syntax</h3>

<pre class="syntaxbox"><strong>Operator:</strong> +x
</pre>

<h3 id="Examples_10">Examples</h3>

<pre class="brush: js">+3     // 3
+'3'   // 3
+true  // 1
+false // 0
+null  // 0
+function(val){ return val } // NaN
</pre>

<h2 id="Specifications">Specifications</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.</td>
  </tr>
  <tr>
   <td>{{SpecName('ES5.1', '#sec-11.3')}}</td>
   <td>{{Spec2('ES5.1')}}</td>
   <td>Defined in several sections of the specification: <a href="http://www.ecma-international.org/ecma-262/5.1/#sec-11.6">Additive operators</a>, <a href="http://www.ecma-international.org/ecma-262/5.1/#sec-11.5">Multiplicative operators</a>, <a href="http://www.ecma-international.org/ecma-262/5.1/#sec-11.3">Postfix expressions</a>, <a href="http://www.ecma-international.org/ecma-262/5.1/#sec-11.4">Unary operators</a>.</td>
  </tr>
  <tr>
   <td>{{SpecName('ES2015', '#sec-postfix-expressions')}}</td>
   <td>{{Spec2('ES2015')}}</td>
   <td>Defined in several sections of the specification: <a href="http://www.ecma-international.org/ecma-262/6.0/#sec-additive-operators">Additive operators</a>, <a href="http://www.ecma-international.org/ecma-262/6.0/#sec-multiplicative-operators">Multiplicative operators</a>, <a href="http://www.ecma-international.org/ecma-262/6.0/#sec-postfix-expressions">Postfix expressions</a>, <a href="http://www.ecma-international.org/ecma-262/6.0/#sec-unary-operators">Unary operators</a>.</td>
  </tr>
  <tr>
   <td>{{SpecName('ES2016', '#sec-postfix-expressions')}}</td>
   <td>{{Spec2('ES2016')}}</td>
   <td>Added <a href="https://github.com/rwaldron/exponentiation-operator">Exponentiation operator</a>.</td>
  </tr>
  <tr>
   <td>{{SpecName('ES2017', '#sec-postfix-expressions')}}</td>
   <td>{{Spec2('ES2017')}}</td>
   <td> </td>
  </tr>
  <tr>
   <td>{{SpecName('ESDraft', '#sec-additive-operators')}}</td>
   <td>{{Spec2('ESDraft')}}</td>
   <td> </td>
  </tr>
 </tbody>
</table>

<h2 id="Browser_compatibility">Browser compatibility</h2>



<p>{{Compat("javascript.operators.arithmetic")}}</p>

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

<ul>
 <li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Assignment_Operators">Assignment operators</a></li>
</ul>