es6用法

Aarry prototypes

forEach for doing a thing with or to every entry in an array; filter for producing a new array containing only qualifying entries; map for making a one-to-one new array by transforming an existing array; some to check whether at least one element in an array fits some description; every to check whether all entries in an array match a description; find to look for a value in an array

e.g.

// map

let arr = [{a:'1'}, {b: '2'}]

arr = arr.map(item => {
    if(item.a=== '1') return Object.assign(item, {c: '3'})
    return item // if not return will get undefined
})

console.log(arr) 
//output
// 0: {a: "1", c: "3"}
// 1: {b: "2"}


// for each

let arr = [{a:'1'}, {b: '2'}]

arr.forEach((item, index, arr)  => {
    if(item.a=== '1') arr[index] = {c: '3'}
})

console.log(arr) 
//output
// 0: {c: "3"}
// 1: {b: "2"}