Some effective JS tips

This article mainly talks about some effective JS tips with you. Friends in need can refer to it. I hope it can help everyone.

1. Ternary operator

When you want to write an if...else statement in the project, if it is not a multiple judgment, You can consider ternary operations instead

let a = 1, answer = null
if( a > 5 ) {
    answer = '大帅比'
}else{ 
    answer = '前端强无敌'
}
简写：answer = a > 5 ?  '大帅比' : '前端强无敌'

2, for simplification (new method provided by ES6)

for(let i = 0; i < arr.length; i++){}
简写：for (let [index, item] of arr.entries()) {
        index为下标，item为每一项内容
}

3, arrow function (es6)

function test （）{ console.info（name） }
setTimeout（function() { console.info(''okay) }， 1500）
arr.forEach(function (item) {    
    console.info(item)
})
简写： let test = （args） => {  console.info(name) }
setTimeout(() => { console.info('okay') }, 1500)
arr.forEach(item => console.info(item))

It seems more convenient, this will not change when the arrow function is used~!

4. Extension operator

Array merging:

const a = [1, 3, 5]
const nums = [2, 4, 6].concat(a);

Array cloning: //Because the array is a reference type, it is often necessary to clone a separate one The operation

const arr = [1, 2, 3, 4]
cons arr2 = arr.slice()
简写： const nums = [2, 4, 6,  ...a]  // [2, 4, ...a, 6]

a can be inserted at any position instead of appending only at the end, which is more convenient than concat!

Used in objects:

const obj =  { a:1 , b:2, c:3,  ...obj2 } =  { a:1 , b:2, c:3,  d:5, e: 6}
obje = {d:5, e: 6}

5. Object attribute abbreviation

When the key value is the same

const obj = {x:x，y:y}
简写：cont obj = {x，y}

6. The abbreviation of the line string

const learn = 'study vue react rn nih\n\t'
                     +  'study vue react rn nih\n\t'
                     +  'study vue react rn nih\n\t'
                     +  'study vue react rn nih\n\t'
                     +  'study vue react rn nih\n\t'
简写：const learn = `study vue react rn nih
                                  study vue react rn nih
                                 study vue react rn nih
                                 study vue react rn nih
                                study vue react rn nih`

7. The template string

const url = 'http://ab.cc.com/' + data + '/beta/info'
简写：const url = `http://ab.cc.com/${data}/beta/info`

${} can be directly put into the variable, which is very easy to use. Easy~remember the backticks! ! !

8. Array.find

If you want to find the required data in an array, you need to loop through it. Find in ES6 can simplify its operation

cont data = [
{'type': 'dog',  'color': 'red'},
{'type': 'cat', 'color: 'white'},
{'type': 'bird', 'color': 'blue'}
]
function findeClor(color) {
        for(let i = 0; i < data.length; i ++ ) {
                if(data[i].type== &#39;cat&#39; && data[i].color== color) {
                        return data[i]
                } 
        }
}
简写：let cat = data.find(item => item.type == &#39;cat&#39; && item.color== &#39;red&#39;)

9. Convert pseudo array to real array (Pseudo array has no interator interface)

let p = document.getElementById('p')

p is a pseudo array and cannot be traversed using methods such as forEach. You can use the more troublesome for loop

let p = Array.from(p)  或者 let p = [...p]

At this time, p is a truly traversable array

10. Array deduplication, Set

let a = [2, 3, 1, 2]

new Set() returns a pseudo array. You need to use the spread operator to convert it into a real array. Array.from() is also good. Selection

let b = [... new Set(a)] // [2, 3, 1]

11. Default parameters

function test(a, b, c = 'Dashuaibi', d = false){

}

test('front-end', 'Beima')

If the two parameters c and d are not passed in, then c defaults to 'Dashuaibi' and d defaults to false

12. Mandatory parameters

JS , if the function does not pass parameters, the parameters will default to undefined. This may cause a program exception, and an exception needs to be thrown

function(data) {
        if(data === undefined) {
                throw new Error('Missing')   
        } 
        return bar
}
简写:
mandatory = () => {
        throw new Erroe ('Missing')
}
foo = (bar = mandatory()) => {
        return bar
}

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