Front end utility operator, some write code operation

JavaScript Art 2021-06-17 19:25:24
end utility operator write code

Some common operators can make your front-end code more concise . This article sorts out some JS The operator used in / The operator , The goal is to simplify the code .

1、?? The operator Null merge / Empty judgment

Null merge operator , If the first parameter is not null perhaps undefined, This operator will return the first parameter , otherwise , It will return the second parameter

null ?? 3 //3
undefined ?? 3 //3
7 ?? 3 //7
2、?. The operator null Transmission symbol ( Or chain decision operator )

stay js, If you read an attribute in an object , It is often necessary to judge whether the object exists first , In case of error .

let a = (obj && || 'default';

The above code can be used null The conduction sign is abbreviated as

let a = obj ?. name || 'default';
3、??= The operator Logical null assignment operator

This assignment operator assigns a new value only if the current value is empty or undefined .

let a = null
const b = 5
console.log(a ??= b) // => 5
console.log(a = (a ?? b)) // => 5
4、 Ternary operator

val It's true , be a Value ifTrue , Otherwise, the value is ifFalse

const a = val ? ifTrue : ifFalse
5、~~ The operator Bitwise operators

You can use a double-digit operator instead of a positive number Math.floor( ), Instead of a negative number Math.ceil( ). The advantage of the double no positioning operator is that it performs the same operation faster .

Math.floor(4.9) === 4 //true
// Shorthand for :
~~4.9 === 4 //true

But be careful , For positive numbers ~~ Operation result and Math.floor( ) The results are the same , And for negative numbers, it's the same as Math.ceil( ) The result is the same :

~~4.5 // 4
Math.floor(4.5) // 4
Math.ceil(4.5) // 5
~~-4.5 // -4
Math.floor(-4.5) // -5
Math.ceil(-4.5) // -4
6、&& And || or Short circuit operator

&& To get a false operation , Judge from left to right , If you encounter a false value , It returns a false value , No more , Otherwise return the last true value

|| To get the truth , Judge from left to right , If you come across a truth value , Return the true value , No more , Otherwise return the last false value

let param1 = expr1 && expr2
let param2 = expr1 || expr2
7、| 0 integer

To a number | 0 It can be rounded , Negative numbers also apply ,num | 0

1.3 | 0 // 1
-1.9 | 0 // -1
8、& 1 Judge odd even number

To a number & 1 We can judge odd and even numbers , Negative numbers also apply ,num & 1

const num=3;
!!(num & 1) // true
!!(num % 2) // true
9、_ Numeric separator

ES2021 The numerical separator is introduced _ , Provide separation between numerical groups , Make a long number easier to read .Chrome Support for numeric separators has been provided , You can try it in your browser .

let number = 100_0000_0000_0000 // 0 It's too much. It's too much to see without a numeric divider
console.log(number) // Output 100000000000000

Besides , The decimal part of the decimal system can also use numeric dividers , Binary system 、 You can also use numeric dividers in hexadecimal

0x11_1 === 0x111 // true Hexadecimal
0.11_1 === 0.111 // true Decimal decimal
0b11_1 === 0b111 // true Binary system
10、void Operator

void Operator Evaluate a given expression , Then return undefined

It can be used to give expressions to functions that are called immediately in use (IIFE) when , You can use void Operator let JS The engine turned one function Keywords are recognized as function expressions instead of function declarations .

function iife() { console.log('foo') }() // Report errors , because JS Engine handle IIFE Identify for function declaration
void function iife() { console.log('foo') }() // Normal call
~function iife() { console.log('foo') }() // You can also use a bit operator
(function iife() { console.log('foo') })() // Or simply use parentheses to express the whole expression

It can also be used in arrow functions to avoid value leakage , Arrow function , It is allowed to return the value directly without using brackets in the function body . This feature brings users a lot of convenience , But sometimes it brings unnecessary trouble , If a function with no return value is called on the right side , When the return value changes , Can cause unexpected side effects .

const func = () => void customMethod() // Especially when passing a function to an event or callback function

Be on the safe side , When you don't want the return value of a function to be anything but null , You should use void To make sure to return undefined, such , When customMethod When the return value changes , And it doesn't affect the behavior of the arrow function .

11、js The priority of the operator

JavaScript Operator priority , Describes the order in which operations are performed when computing expressions . Perform operations with higher priority first , Then perform lower priority operations . for example , We often say to perform multiplication and division first , And then add and subtract .

Parentheses are used to change the order of computation determined by the priority of the operator . That is to say , First calculate the expression in parentheses , Then use its value for the rest of the expression .

In fact, in the process of calculation , Like any other language , It's better to put parentheses directly , Such as var a = 1; a = (a + 100) >>(a+1); and var a = 1; a = a + 100>>a+1; The result is 25, The order of operation is the same , The readability of the front is better ?

This article is from WeChat official account. - javascript art (gh_4e5484fd6b52) , author :zhangjing

The source and reprint of the original text are detailed in the text , If there is any infringement , Please contact the [email protected] Delete .

Original publication time : 2021-05-14

Participation of this paper Tencent cloud media sharing plan , You are welcome to join us , share .

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