Example explanation of remaining parameters in ES6-JS Tutorial-php.cn

Example explanation of remaining parameters in ES6

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Release： 2018-11-14 15:38:30

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The content of this article is about the code explanation of the remaining parameters in ES6. It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

Overview

The remaining parameters aggregate parameters without corresponding formal parameters into an array

Syntax

function(a, b, ...theArgs) {
}

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Only aggregate parameters that do not correspond to formal parameters

The remaining parameters will only aggregate parameters without corresponding formal parameters into an array, while arguments contains all parameters.

function add(a, b, ...theArgs) {
    return {rest: theArgs, arguments}
}
add() 
// {rest: [undefined, undefined, []], arguments: Arguments(0)}
add(1) 
// {rest: [1, undefined, []], arguments: Arguments(1)}
add(1, 2) 
// {rest: [1, 2, []], arguments: Arguments(2)}
add(1, 2, 3, 4, 5) 
// {rest: [1, 2, [3, 4, 5]], arguments: Arguments(5)}

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The remaining parameters are arrays

The remaining parameters are always an array, unlike arguments which is a pseudo-array

function add(...theArgs) {
    console.log(Array.isArray(theArgs))
    theArgs.forEach((a)=>console.log(a))
    console.log(Array.isArray(arguments))
    Array.prototype.slice.call(arguments, add.length).forEach((a)=>console.log(a)) // 转化成数组
}
add(1,2,3) // true 1 2 3 false 1, 2, 3, 4

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Deconstructing the remaining parameters

function add(...[a, b, c]){
    return a + b +c
}
add(1, 2, 3) // 6
add(1, 2, 3) // 6

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Use `babel`Translation

function add(...num){
  return num.reduce((n1,n2)=>n1+n2)
}

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After translation

function add() {
  for (var _len = arguments.length, num = Array(_len), _key = 0; _key < _len; _key++) {
    num[_key] = arguments[_key];
  }

  return num.reduce(function (n1, n2) {
    return n1 + n2;
  });
}

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