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ES6 learning let&const juejin.cn/post/684490…

. Operator definition

. The operator is also called the expansion collection operator. . Operators have different roles in different places. 1. Write ———— collection function

function test(... Arg) {} the test (1, 2, 3)Copy the code

2. Read ———— to expand the function

Var arg = [1,2,3] console.log(... arg) //1 2 3Copy the code

. Operator action

1. Simplify writing length 2. Improve development efficiency

Write expansion

Undefined arguments can be accepted, using arguments and… The sum of the indeterminate arguments by the operator.

Function sum() {// Arguments let sumNumber = 0 for(let I = 0; i < arguments.length; I ++) {sumNumber += arguments[I]} console.log(sumNumber) // 15 return sumNumber} sum(1,2,3,4,5) function sum(... Arg) {// Use... Operator console.log(arg) //[1, 2, 3, 4, 5] arg is an array, ForEach (function(ele) {sumNumber += ele}) console.log(sumNumber) // 15 return SumNumber} sum (1, 2, 3, 4, 5)Copy the code

It can be seen that using… Operators are more concise.

. Operators can be preceded by fixed parameters, and values can be passed in. But… Operators are not allowed to pass in parameters.

function test(a,b,... Arg) {the console. The log (a, b, arg) / / 10 20 [" aa ", "bb"]} the test (10, 20, 'aa', 'bb')Copy the code

The following code uses… The operator writes an average value minus the highest value and minus the lowest value

function average(... arg) { arg.sort(function(a,b) { return a - b }) arg.pop() arg.shift() console.log(arg) //[2, 3, 4, 5, 6] return computedScore(... arg) } function computedScore(... arg) { let sum = 0 arg.forEach(function (ele) { sum += ele }) console.log(sum/arg.length) //4 return sum/arg.length } Business (1,2,3,4,5,6,7)Copy the code

It can be seen that using… Operators are obviously more convenient than arguments.

Reading expansion

. [1,2,3,4,5] is equivalent to 1,2,3,4,5

Let arr1 = [1,2,3,4,5] let arr2 = [6,7,8] let newArr = [...arr1,...arr2] //[].concat(arr1,arr2) console.log(newArr) //[1, 2, 3, 4, 5, 6, 7, 8] corresponds to concatCopy the code

In the ES6… Operators operate primarily on arrays, and in ES7 you can expand objects without going into too much detail here.

Welcome to point out any mistakes, thanks for watching.

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