算术运算符以数值(字面量或变量)作为其操作数,并返回一个单个数值。标准算术运算符是加法(+),减法( - ),乘法(*)和除法(/)。
加法 (+)
加法运算符的作用是数值求和,或者字符串拼接。
语法
运算符: x + y
示例
// Number + Number -> 数字相加 1 + 2 // 3 // Boolean + Number -> 数字相加 true + 1 // 2 // Boolean + Boolean -> 数字相加 false + false // 0 // Number + String -> 字符串连接 5 + "foo" // "5foo" // String + Boolean -> 字符串连接 "foo" + false // "foofalse" // String + String -> 字符串连接 "foo" + "bar" // "foobar"
减法 (-)
减法运算符使两个操作数相减,结果是它们的差值。
语法
运算符: x - y
示例
5 - 3 // 2 3 - 5 // -2 "foo" - 3 // NaN
除法 (/)
除法运算符的结果是操作数的商 ,左操作数是被除数,右操作数是除数。
语法
运算符: x / y
示例
1 / 2 // 在 JavaScript 中返回 0.5 1 / 2 // 在 Java 中返回 0 // (不需要数字是明确的浮点数) 1.0 / 2.0 // 在 JavaScript 或 Java 中都返回 0.5 2.0 / 0 // 在 JavaScript 中返回 Infinity 2.0 / 0.0 // 同样返回 Infinity 2.0 / -0.0 // 在 JavaScript 中返回 -Infinity
乘法 (*)
乘法运算符的结果是操作数的乘积。
语法
运算符: x * y
示例
2 * 2 // 4 -2 * 2 // -4 Infinity * 0 // NaN Infinity * Infinity // Infinity "foo" * 2 // NaN
求余 (%)
求余运算符返回第一个操作数对第二个操作数的模,即 var1
对 var2
取模,其中 var1
和 var2
是变量。取模功能就是 var1
除以 var2
的整型余数。 以前有个提议,在ECMAScript未来的版本中,可能会有一个获取实际模的运算符。
语法
运算符: var1 % var2
示例
12 % 5 // 2 -1 % 2 // -1 NaN % 2 // NaN 1 % 2 // 1 2 % 3 // 2 -4 % 2 // -0 5.5 % 2 // 1.5
幂 (**)
幂运算符返回第一个操作数做底数,第二个操作数做指数的乘方。即, var1
var2
,其中 var1
和 var2
是其两个操作数。幂运算符是右结合的。a ** b ** c
等同于 a ** (b ** c)
。
语法
运算符: var1 ** var2
注解
包括 PHP 或 Python 等的大多数语言中,都包含幂运算符(一般来说符号是 ^ 或者 **)。这些语言中的幂运算符有着比其他的单目运算符(如一元 + 或一元 - )更高的优先级。但是作为例外,在 Bash 中,** 运算符被设计为比单目运算符优先级更低。在最新的 JavaScript(ES2016) 中,禁止使用带歧义的幂运算表达式。比如,底数前不能紧跟一元运算符(+/-/~/!/delete/void/typeof
)
-2 ** 2; // 在 Bash 中等于 4 ,而在其他语言中一般等于 -4 // 在 JavaScript 中是错误的,因为这会有歧义 -(2 ** 2); // -4 在JavaScript中能够明显体现出作者的意图
示例
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
如果要反转求幂表达式结果的符号,你可以采用这样的方式:
-(2 ** 2) // -4
强制求幂表达式的基数为负数:
(-2) ** 2 // 4
递增 (++)
递增运算符为其操作数增加1,返回一个数值。
- 如果后置(postfix)使用,即运算符位于操作数的后面(如 x++),那么将会在递增前返回数值。
- 如果前置(prefix)使用,即运算符位于操作数的前面(如 ++x),那么将会在递增后返回数值。
语法
运算符: x++ 或者 ++x
示例
// 后置 var x = 3; y = x++; // y = 3, x = 4 // 前置 var a = 2; b = ++a; // a = 3, b = 3
递减 (--)
递减运算符将其操作数减去1,并返回一个数值。
- 如果后置使用(如 x--),则在递减前返回数值。
- 如果前置使用(如 --x),则在递减后返回数值。
语法
运算符: x-- or --x
示例
// 后置 var x = 3; y = x--; // y = 3, x = 2 // 前置 var a = 2; b = --a; // a = 1, b = 1
一元负号 (-)
一元负号运算符位于操作数前面,并转换操作数的符号。
语法
运算符: -x
示例
var x = 3; y = -x; // y = -3, x = 3
一元正号 (+)
一元正号运算符位于其操作数前面,计算其操作数的数值,如果操作数不是一个数值,会尝试将其转换成一个数值。 尽管一元负号也能转换非数值类型,但是一元正号是转换其他对象到数值的最快方法,也是最推荐的做法,因为它不会对数值执行任何多余操作。它可以将字符串转换成整数和浮点数形式,也可以转换非字符串值 true
,false
和
null
。小数和十六进制格式字符串也可以转换成数值。负数形式字符串也可以转换成数值(对于十六进制不适用)。如果它不能解析一个值,则计算结果为 NaN。
语法
运算符: +x
示例
+3 // 3 +"3" // 3 +true // 1 +false // 0 +null // 0 +function(val){ return val;} //NaN
规范
Specification | Status | Comment |
---|---|---|
ECMAScript 1st Edition (ECMA-262) | Standard | Initial definition. |
ECMAScript 5.1 (ECMA-262) | Standard | Defined in several sections of the specification: Additive operators, Multiplicative operators, Postfix expressions, Unary operators. |
ECMAScript 2015 (6th Edition, ECMA-262) | Standard | Defined in several sections of the specification: Additive operators, Multiplicative operators, Postfix expressions, Unary operators. |
ECMAScript 2016 (ECMA-262) | Standard | Added Exponentiation operator. |
ECMAScript 2017 (ECMA-262) | Standard | |
ECMAScript Latest Draft (ECMA-262) | Draft |
浏览器兼容
The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.
Desktop | Mobile | Server | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Addition (+ ) |
Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 3 | Opera Full support Yes | Safari Full support Yes | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
Decrement (-- ) |
Chrome Full support 2 | Edge Full support 12 | Firefox Full support 1 | IE Full support 3 | Opera Full support Yes | Safari Full support Yes | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
Division (/ ) |
Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 3 | Opera Full support Yes | Safari Full support Yes | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
Exponentiation (** ) |
Chrome Full support 52 | Edge Full support 14 | Firefox Full support 52 | IE No support No | Opera Full support Yes | Safari Full support 10.1 | WebView Android Full support 51 | Chrome Android Full support 52 | Firefox Android Full support 52 | Opera Android Full support Yes | Safari iOS Full support 10.3 | Samsung Internet Android Full support 6.0 | nodejs Full support 7.0.0
|
Increment (++ ) |
Chrome Full support 2 | Edge Full support 12 | Firefox Full support 1 | IE Full support 3 | Opera Full support Yes | Safari Full support Yes | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
Multiplication (* ) |
Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 3 | Opera Full support Yes | Safari Full support Yes | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
Remainder (% ) |
Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 3 | Opera Full support Yes | Safari Full support Yes | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
Subtraction (- ) |
Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 3 | Opera Full support Yes | Safari Full support Yes | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
Unary negation (- ) |
Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 3 | Opera Full support Yes | Safari Full support Yes | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
Unary plus (+ ) |
Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 3 | Opera Full support Yes | Safari Full support Yes | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
Legend
- Full support
- Full support
- No support
- No support
- User must explicitly enable this feature.
- User must explicitly enable this feature.