ES6 new - function part

Function extension

1.es6 Parameter extension :

(1) The default value is

(2) Variable parameters

2.es6 New arrow function in

1, grammar :const Function name = () => {  }

2. characteristic :

3. Be careful : Cannot pass new Key word call

4, application : It is mostly used in callback functions and changes this When pointing

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Function extension

1.es6 Parameter extension :

(1) The default value is

In the default position of formal parameters , Assign value by single equal sign , Only the parameters are not transmitted and the parameters are undefined Go to the default value

function add(x=10,y=20){ return x+y }

console.log(add(10,10)) //20

console.log(add(' ',0)) // " 0 "

console.log(add(undefined,10)) //20

(2) Variable parameters

 ...args Collect the remaining parameters args: Parameter name

Be careful : ...args True array ,es5 in arguments Is a pseudo array

Be careful :... Only once ; ... It can only be placed in the last formal parameter position ; ... There can be one or more fixed position parameters in front

function getSum(...args){ console.log(args) }

console.log(1,2,3,4,5) // Output [1,2,3,4,5]

function getArr( ...args,...rest){} // Two ... At the same time , Will report a mistake

function getSum(num,..args){ console.log(num,args)}

console.log(gerSum(100,1,2,3,4,5)) // Output :100,[1,2,3,4,5]

2.es6 New arrow function in

1, grammar :const Function name = () => {  }

2. characteristic :

(1) When there is only one formal parameter , You can omit parentheses

(2) When the function body has only one sentence , You can omit the braces , If braces are omitted , Arrow function comes with return function , No more writing

(3) Inside the arrow function this Points to this

3. Be careful : Cannot pass new Key word call

4, application : It is mostly used in callback functions and changes this When pointing

Ordinary function const fu = function(){ }

Arrow function const fn=()=>{ The body of the function } fn()

const sayHi = function(name){ return `hi${this.name}`}

const sayHi = (name)=>{ `hi${this.name}` }         sayHi("aa")