Rest parameters and spread operator in ES6

 This article mainly introduces the usage of ES6 spread operator and rest operator, and analyzes the basic functions, usage and operation precautions of ES6 spread operator and rest operator in combination with examples.

The rest parameter was introduced in ES6 to obtain the actual parameters of the function, which is used to replace the arguments, and is placed in the last parameter when used，Below are some use cases for rest parameters.The rest parameter is placed in the function declaration when used, and the spread operator is placed in the formal parameter when the function is called, using the symbol "...".

• basic use

function fun1(){

    console.log(arguments);

}

function fun2(...args){

    console.log(args);

}

fun1(1,2,3);

fun2(1,2,3);

let arr=[1,2,3];

function fun1(){

    console.log(arguments);

}

function fun2(){

    console.log(arguments);

}

fun1(arr);

fun2(...arr);

• Spread operator - merging of arrays:

let arr1=[1,2,3];

let arr2=[4,5,6];

let arr3=[...arr1,...arr2];

// arr1.push(...arr2);

//arr1.concat(arr2);

// console.log(arr1);

/* console.log(arr1);

arr1.forEach((val)=>{

    console.log(val)

}) */

console.log(arr3);

• Spread operator - clone of array:

let arr1=[1,2,3];

let arr2=[...arr1];

console.log(arr2);

• Spread operator - turns a pseudo-array into a real array:
• Spread operator - converts a string to an array: