From 33058f2b292b3a581333bdfb21b8f671898c5060 Mon Sep 17 00:00:00 2001 From: Peter Bengtsson Date: Tue, 8 Dec 2020 14:40:17 -0500 Subject: initial commit --- .../operators/assignment_operators/index.html | 412 +++++++++++++++++++++ 1 file changed, 412 insertions(+) create mode 100644 files/zh-cn/web/javascript/reference/operators/assignment_operators/index.html (limited to 'files/zh-cn/web/javascript/reference/operators/assignment_operators') diff --git a/files/zh-cn/web/javascript/reference/operators/assignment_operators/index.html b/files/zh-cn/web/javascript/reference/operators/assignment_operators/index.html new file mode 100644 index 0000000000..5d500538b4 --- /dev/null +++ b/files/zh-cn/web/javascript/reference/operators/assignment_operators/index.html @@ -0,0 +1,412 @@ +--- +title: 赋值运算符 +slug: Web/JavaScript/Reference/Operators/Assignment_Operators +tags: + - JavaScript + - 运算符 +translation_of: Web/JavaScript/Reference/Operators#Assignment_operators +--- +
{{jsSidebar("Operators")}}
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赋值运算符(assignment operator)基于右值(right operand)的值,给左值(left operand)赋值。

+ +
{{EmbedInteractiveExample("pages/js/expressions-assignment.html")}}
+ + + +

概述

+ +

基本的赋值运算符是等号(=),该运算符把它右边的运算值赋给左边。即,x = y 把 y 的值赋给 x。 其他的赋值运算符通常是标准运算符的简写形式,如下面的定义与示例。 

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名称简写形式含义
赋值(Assignment)x = yx = y
加赋值(Addition assignment)x += yx = x + y
减赋值(Subtraction assignment)x -= yx = x - y
乘赋值(Multiplication assigment)x *= yx = x * y
除赋值(Division assignment)x /= yx = x / y
模赋值(Remainder assignment)x %= yx = x % y
指数赋值(Exponentiation assignment)x **= yx = x ** y
左移赋值(Left shift assignment)x <<= yx = x << y
右移赋值(Right shift assignment)x >>= yx = x >> y
无符号右移赋值(Unsigned right shift assignment)x >>>= yx = x >>> y
按位与赋值(Bitwise AND assignment)x &= yx = x & y
按位异或赋值(Bitwise XOR assignment)x ^= yx = x ^ y
按位或赋值(Bitwise OR assignment)x |= yx = x | y
+ +

赋值

+ +

简单的赋值运算符,把一个值赋给一个变量。为了把一个值赋给多个变量,可以以链式使用赋值运算符。参考下例:

+ +

语法

+ +
Operator: x = y
+
+ +

示例

+ +
// Assuming the following variables
+//  x = 5
+//  y = 10
+//  z = 25
+
+x = y     // x is 10
+x = y = z // x, y and z are all 25
+
+ +

加赋值(Addition assignment)

+ +

加赋值运算符把一个右值与一个变量相加,然后把相加的结果赋给该变量。两个操作数的类型决定了加赋值运算符的行为。算术相加或字符串连接都有可能。更多细节参考 {{jsxref("Operators/Arithmetic_Operators", "addition operator", "#Addition", 1)}}。

+ +

语法

+ +
Operator: x += y
+Meaning:  x  = x + y
+
+ +

示例

+ +
// 定义下列变量
+//  foo = 'foo'
+//  bar = 5
+//  baz = true
+
+
+// Number + Number -> addition
+bar += 2 // 7
+
+// Boolean + Number -> addition
+baz += 1 // 2
+
+// Boolean + Boolean -> addition
+baz += false // 1
+
+// Number + String -> concatenation
+bar += 'foo' // "5foo"
+
+// String + Boolean -> concatenation
+foo += false // "foofalse"
+
+// String + String -> concatenation
+foo += 'bar' // "foobar"
+
+ +

减赋值(Subtraction assignment)

+ +

减赋值运算符使一个变量减去右值,然后把结果赋给该变量。更多细节查看 {{jsxref("Operators/Arithmetic_Operators", "subtraction operator", "#Subtraction", 1)}} 。

+ +

语法

+ +
Operator: x -= y
+Meaning:  x  = x - y
+
+ +

示例

+ +
// 假定已定义了下面的变量
+//  bar = 5
+
+bar -= 2     // 3
+bar -= "foo" // NaN
+
+ +

乘赋值(Multiplication assignment)

+ +

乘赋值运算符使一个变量乘以右值,然后把相成的结果赋给该变量。更多细节查看 {{jsxref("Operators/Arithmetic_Operators", "multiplication operator", "#Multiplication", 1)}}。

+ +

语法

+ +
Operator: x *= y
+Meaning:  x  = x * y
+
+ +

示例

+ +
// 假定已定义了下面的变量
+//  bar = 5
+
+bar *= 2     // 10
+bar *= 'foo' // NaN
+
+ +

除赋值(Division assignment)

+ +

除赋值运算符使一个变量除以右值,然后把结果赋给该变量。更多细节查看 {{jsxref("Operators/Arithmetic_Operators", "division operator", "#Division", 1)}}。

+ +

语法

+ +
Operator: x /= y
+Meaning:  x  = x / y
+
+ +

示例

+ +
// 假定已定义了下面的变量
+//  bar = 5
+
+bar /= 2     // 2.5
+bar /= "foo" // NaN
+bar /= 0     // Infinity
+
+ +

模赋值(Remainder assignment)

+ +

模赋值运算符使一个变量除以右值,然后把余数赋给该变量。更多细节查看 {{jsxref("Operators/Arithmetic_Operators", "remainder operator", "#Remainder", 1)}}。

+ +

语法

+ +
Operator: x %= y
+Meaning:  x  = x % y
+
+ +

示例

+ +
// Assuming the following variable
+//  bar = 5
+
+bar %= 2     // 1
+bar %= 'foo' // NaN
+bar %= 0     // NaN
+
+ +

指数赋值(Exponentiation assignment)

+ +

指数赋值运算符使一个变量为底数、以右值为指数的指数运算(乘方)结果赋给该变量。更多细节查看 {{jsxref("Operators/Arithmetic_Operators", "算术运算符", "#Exponentiation", 1)}}。

+ +

语法

+ +
语法: x **= y
+含义:  x  = x ** y
+
+ +

示例

+ +
// Assuming the following variable
+//  bar = 5
+
+bar **= 2     // 25
+bar **= 'foo' // NaN
+ +

左移赋值(Left shift assignment)

+ +

左移赋值运算符使变量向左移动指定位数的比特位,然后把结果赋给该变量。更多细节查看 {{jsxref("Operators/Bitwise_Operators", "left shift operator", "#Left_shift", 1)}}。

+ +

语法

+ +
Operator: x <<= y
+Meaning:  x   = x << y
+
+ +

示例

+ +
var bar = 5; //  (00000000000000000000000000000101)
+bar <<= 2; // 20 (00000000000000000000000000010100)
+
+ +

右移赋值(Right shift assignment)

+ +

右移赋值运算符使变量向右移指定位数的比特位,然后把结果赋给该变量。更多细节查看 {{jsxref("Operators/Bitwise_Operators", "right shift operator", "#Right_shift", 1)}}。

+ +

语法

+ +
Operator: x >>= y
+Meaning:  x   = x >> y
+
+ +

示例

+ +
var bar = 5; //   (00000000000000000000000000000101)
+bar >>= 2;   // 1 (00000000000000000000000000000001)
+
+var bar = -5; //    (-00000000000000000000000000000101)
+bar >>= 2;  // -2 (-00000000000000000000000000000010)
+
+ +

无符号右移赋值(Unsigned right shift assignment)

+ +

无符号右移赋值运算符向右移动指定数量的比特位,然后把结果赋给变量。更多细节查看 {{jsxref("Operators/Bitwise_Operators", " unsigned right shift operator", "#Unsigned_right_shift", 1)}}。

+ +

语法

+ +
Operator: x >>>= y
+Meaning:  x    = x >>> y
+
+ +

示例

+ +
var bar = 5; //   (00000000000000000000000000000101)
+bar >>>= 2;  // 1 (00000000000000000000000000000001)
+
+var bar = -5; // (-00000000000000000000000000000101)
+bar >>>= 2; // 1073741822 (00111111111111111111111111111110)
+ +

按位与赋值(Bitwise AND assignment)

+ +

按位与赋值运算符使用两个操作值的二进制表示,执行按位与运算,并把结果赋给变量。更多细节查看 {{jsxref("Operators/Bitwise_Operators", "bitwise AND operator", "#Bitwise_AND", 1)}}。

+ +

语法

+ +
Operator: x &= y
+Meaning:  x  = x & y
+
+ +

示例

+ +
var bar = 5;
+// 5:     00000000000000000000000000000101
+// 2:     00000000000000000000000000000010
+bar &= 2; // 0
+
+ +

按位异或赋值(Bitwise XOR assignment)

+ +

按位异或赋值运算符使用两个操作值的二进制表示,执行二进制异或运算,并把结果赋给变量。更多细节查看 {{jsxref("Operators/Bitwise_Operators", "bitwise XOR operator", "#Bitwise_XOR", 1)}}。

+ +

语法

+ +
Operator: x ^= y
+Meaning:  x  = x ^ y
+
+ +

示例

+ +
var bar = 5;
+bar ^= 2; // 7
+// 5: 00000000000000000000000000000101
+// 2: 00000000000000000000000000000010
+// -----------------------------------
+// 7: 00000000000000000000000000000111
+
+ +

按位或赋值(Bitwise OR assignment)

+ +

按位或赋值运算符使用两个操作值的二进制表示,执行按位或运算,并把结果赋给变量。更多细节查看 {{jsxref("Operators/Bitwise_Operators", "bitwise OR operator", "#Bitwise_OR", 1)}}。

+ +

语法

+ +
Operator: x |= y
+Meaning:  x  = x | y
+
+ +

示例

+ +
var bar = 5;
+bar |= 2; // 7
+// 5: 00000000000000000000000000000101
+// 2: 00000000000000000000000000000010
+// -----------------------------------
+// 7: 00000000000000000000000000000111
+
+ +

示例

+ +

带有赋值运算符的左值(Left operand)

+ +

在某些不常见的情况下,赋值运算符(如 x += y)并不等同于表达式( x = x + y)。当一个赋值运算符的左值包含有一个赋值运算符时,左值只会被求值一次。例如:

+ +
a[i++] += 5         // i 执行一次求值
+a[i++] = a[i++] + 5 // i 执行两次求值
+
+ +

规范

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SpecificationStatusComment
{{SpecName('ESDraft', '#sec-assignment-operators', 'Assignment operators')}}{{Spec2('ESDraft')}}
{{SpecName('ES2015', '#sec-assignment-operators', 'Assignment operators')}}{{Spec2('ES2015')}}
{{SpecName('ES5.1', '#sec-11.13', 'Assignment operators')}}{{Spec2('ES5.1')}}
{{SpecName('ES1', '#sec-11.13', 'Assignment operators')}}{{Spec2('ES1')}}Initial definition.
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浏览器兼容性

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{{Compat("javascript.operators.assignment")}}

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相关链接

+ + -- cgit v1.2.3-54-g00ecf