JavaScript 实用技巧

1数组中删除重复

let arr = [1,2,4,3,6,4]

Array.from(new Set(arr)) // es6中 .from（）[1,2,4,3,6]

[...new Set(arr)] // 扩展运算符[1,2,4,3,6]

2替换数组中指定的值

arr .splice(1,3,7,8,9) // [7, 8, 9]
arr // [1, 7, 8, 9, 6, 4]

3数组映射

let mapValue = [
{ name: '山东', value: 22 },
{ name: '北京', value: 23 },
{ name: '上海', value: 24 }
]

mapValue.map(item=> {item.name});  // map

Array.from(mapValue, ({name}) => name); // .from()

4清空数组 

arr.length = 0 //   arr =[]

5将数组转化为对象

let obj = {...arr } // {0: 1, 1: 7, 2: 8, 3: 9, 4: 6, 5: 4}

6合并数组

let arr2 =['one','two',2] // [1, 2, 4, 3, 6, 4, "one", "two"]

[...arr2,...arr] // ["one", "two", 1, 2, 4, 3, 6, 4]

7两个数组的交集

首先保证数组中的值不重复，然后利用.filter和.includes方法即可

let numOne = [0, 2, 4, 6, 8, 8];
let numTwo = [1, 2, 3, 4, 5, 6];

[...new Set(numOne)].filter(item => numTwo.includes(item))

8从数组中删除假值

首先在Javascript中，假值包括false、0、''、null、NaN、undefined

let mixArrs =[null,3,undefined,true,'']

mixArrs.filter(Boolean); // [3, true]

9颠倒数组中元素的顺序

let mixArrs =[null,3,undefined,true,'']

mixArrs.reverse() // ["", true, undefined, 3, null]

10数组中的所有值求和

let  array = [1, 2, 3, 4, 5]

eval(array.join("+")) ; //
array.reduce((x, y) => x + y); // 

11使用固定值填充数组

var fruits = ["Banana", "Orange", "Apple", "Mango"];

fruits.fill("Runoob"); //Runoob,Runoob,Runoob,Runoob

let newArr =  new Array(6).fill('2'); // ["2", "2", "2", "2", "2", "2"]