Arithmetic operators

1.1 number operation

1.1.1 Addition, subtraction, multiplication and division

9 / 0 //Infinity
-9 / 0 //-Infinity
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1.1.2 to take more than

-1 % 7 // 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1
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1.1.3 index

7六四屠杀3 / / 343
7六四屠杀2 / / 49
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1.1.4 Autoincrement autodecrement

var a = 10
a++ //a increases by 1, but the expression a++ is 10, taken from the value before the increment
++a //a is incremented by 1, but the expression ++a is 11

a--// same as a++
--a// Same as ++a
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Use autoincrement and subtraction as little as possible, use a+=1,a-=1

1.2 the string operation

Strings support only the plus sign operation

'123'+'456' / / '123456'
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JS some weird points:

1 + '2' //'3', JS converts 1 to string and adds
3 - '2'  //1, JS converts the string to a number and subtracts it
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Comparison operators

= = =

  • The basic type looks at whether the values are equal

  • Object to see if addresses are equal

    [] [] = = =False, the address of the first empty array is different from the address of the second empty array= = = {} {}//false
NaN! = =NaN // Remember the exceptions
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Boolean operators

a = a || 100 // a is 100
console && console.log && console.log('hi') // Prevent console error

function add(n=0){
    return n+1
}// If n is null or undefined, set n to 0 (new syntax)
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Binary operators

4.1 or operators

| as long as there is one of two binary is 1, it returns 1, otherwise it returns 0.

  (0b1111 | 0b1010).toString(2) / / '1111'
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4.2 and operators

& If both bits are 1, the result is 1, otherwise 0

0 & 3 // 0,0 (binary 00) and 3 (binary 11) perform binary sum to get 00.
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4.3 No operator

The binary no operator (~) changes each binary bit to the opposite value (0 to 1,1 to 0).

~ 3 / / - 4
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Three forms of 32-bit integer is 00000000000000000000000000000011, whether the binary operation after 11111111111111111111111111111100.

Since the first digit is 1, the number is a negative number. JavaScript internally uses the form of complement to represent negative numbers, which means that you need to subtract 1 from the number, negate it again, and then add a negative sign to get the corresponding decimal value. This number minus 1 equals 11111111111111111111111111111011, get 00000000000000000000000000000100, take again the plus minus sign is – 4.

And since it’s a little bit of a hassle to do that, you can just remember that if you add something to its negative value, it’s equal to negative 1.

4.4 XOR operators

Two binary bits return 1 if they are different and 0 if they are the same.

0 ^ 3 // 3 0 (binary 00) and 3 (binary 11) perform xOR, each of which is different, so we get 11.
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4.5 Left shift operator

The left-shift operator (<<) moves the binary value of a number to the left by a specified number of digits, terminating with 0, multiplied by 2 to the specified power. When you move to the left, the highest sign bit moves together.

4 << 1
/ / 8

-4 << 1
/ / - 8
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4.6 Right shift operator

The right-shift operator (>>) moves the binary value of a number to the right by a specified number of digits. If it’s positive, add zeros to all the heads; If it’s negative, add 1’s to all the heads

-4 >> 1
/ / - 2
/ * / / for binary form for 11111111111111111111111111111100-4, / / moves to the right one, head to fill 1, 11111111111111111111111111111110, / / is the decimal - 2 * /
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4.7 Right shift operator for header zeroing

The only difference between the right shift operator (>>>) and the right shift operator (>>) is that when the binary form of a number moves to the right, the head is filled with zeros regardless of the sign bit.

-4 >>> 1
/ / 2147483646
/ * / / for binary form for 11111111111111111111111111111100-4, / / take the sign bit moves to the right one, you get 01111111111111111111111111111110, // The decimal value is 2147483646. * /
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4.7 Application of binary symbol bits

4.7.1 use ~ ~ > >, < <, > > >, | to rounded

console.log(~~ 6.83)  / / 6
console.log(6.83>>0)/ / 6
console.log(6.83<<0)/ / 6
console.log(6.83|0)/ / 6
console.log(6.83 >>>0)/ / 6
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4.7.2 Use the and operator to judge odd and even

Use the and operator to determine if it is even

Even number &0b001 = 0Odd number &0b001 = 1
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4.7.3 Exchange values using xOR operations

Xor operations can interchange the values of two variables

var a = 10;
var b = 99;

a ^= b, b ^= a, a ^= b;

a / / 99
b / / 10
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Other operators

5.1 Dot operators

Grammar:

Property name = property value// To read the property value of the object
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However, in JS you can have property values that are not objects

var a = 1 
a.toString() / / '1'

/* If the dot is not preceded by an object, JS will encapsulate it as an object. Number will become number. String will become string. Bool will become Boolean

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5.2 void operator

Grammar:

voidExpression or statementVoid is used to evaluate expressions or execute statements, but void is always undefined
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5.3 Comma operators

Grammar:

expression1The expression2. , expression n// take the value of the expression n as the whole value
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let a = (1.2.3.4.5) // The value of a is 5
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The precedence of the operator

There are 20 operators in total, summarized in MDN

  • The parentheses have the highest precedence, so there is no need to remember anything else