# JavaScript 中的数学运算符 – JavaScript 完全手册（2018版）

### 算术运算符

#### 相加 (+)

const three = 1 + 2
const four = three + 1

const three = 1 + 2
three + 1 // 4
'three' + 1 // three1

#### 相减(-)

const two = 4 - 2

#### 除法(/)

const result = 20 / 5 //result === 4
const result = 20 / 7 //result === 2.857142857142857

1 / 0 //Infinity
-1 / 0 //-Infinity

#### 取余(%)

const result = 20 % 5 //result === 0
const result = 20 % 7 //result === 6

1 % 0 //NaN
-1 % 0 //NaN

1 * 2 //2
-1 * 2 //-2

1 ** 2 //1
2 ** 1 //2
2 ** 2 //4
2 ** 8 //256
8 ** 2 //64

let x = 0
x++ //0
x //1
++x //2

let x = 0
x-- //0
x //-1
--x //-2

let x = 2
-x //-2
x //2

let x = 2
+x //2

x = '2'
+x //2

x = '2a'
+x //NaN

+=：加法赋值
-=：除法赋值
*=：乘法赋值
/=：除法赋值
%=：取余赋值
**=：求幂赋值

const a = 0
a += 5 //a === 5
a -= 2 //a === 3
a *= 2 //a === 6
a /= 2 //a === 3
a %= 2 //a === 1

### 优先级

const a = 1 * 2 + 5 / 2 % 2

• - + ++ -- 一元运算符，递增，递减
• * / % 乘法/除法
• + - 加法/减法
• = += -= *= /= %= **= 赋值运算

const a = 1 * 2 + 5 / 2 % 2
const a = 1 * 2 + 5 / 2 % 2
const a = 2 + 2.5 % 2
const a = 2 + 0.5
const a = 2.5

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