js数组常用方法整理

js中数组常用方法整理

concat

concat用于连接（合并）两个或更多的数组

let a = [1,2,3];
let b = [2,3];
let c = [4];

console.log(a.concat(b,c));//[1, 2, 3, 2, 3, 4]

filter

filter用户对数组进行筛选，筛选出符合条件的选项，返回一个新的数组

let persons = [
	{name:"张三",age:20},
	{name:"李四",age:18},
	{name:"王五",age:20},
	{name:"马六",age:22},
];

let list = persons.filter((item,index,arr)=>{
	//筛选age>20的选项
	return item.age > 20;
})
console.log(list);//[{name:"马六",age:22}]

find

find方法用于查找数组中是否包含某一项
fin在返回true时，会终止函数执行

let persons = [
	{name:"张三",age:20},
	{name:"李四",age:18},
	{name:"王五",age:20},
	{name:"马六",age:22},
	{name:"李四",age:18},
];

let person = persons.find((item,index,arr)=>{
	return item.age == 18;
})

console.log(person);//{name: "李四", age: 18}

finIndex

findIndex与find方法类似，只不过findIndex是返回符合条件的元素的索引

let persons = [
	{name:"张三",age:20},
	{name:"李四",age:18},
	{name:"王五",age:20},
	{name:"马六",age:22},
	{name:"李四",age:18},
];

let person = persons.findIndex((item,index,arr)=>{
	return item.age == 18;
})

console.log(person);//1

includes

includes用来检测数组中是否包含某一项，返回true或者false

let arr = [1,2,3,4,5];

console.log(arr.includes(6));//false

indexOf

用于返回数组中某一项所在的位置，如果没找到，会返回 -1

let arr = [1,2,3,4,5];

console.log(arr.indexOf(3));//2
console.log(arr.indexOf(6));//-1

isArray

用于判断一个对象是否是数组

let a = {name:1,age:22};
let b = [1,3,4];
console.log(Array.isArray(a));//false
console.log(Array.isArray(b));//true

join

用于把一个数组转为字符串，默认用逗号分割，可以传入指定分隔符

let a = [1,2,3,4];

console.log(a.join());//1,2,3,4

console.log(a.join('@'));//1@2@3@4

map

map方法用于对原数组进行处理，并返回一个新的数组，顺序与原始数组一致

let a = [1,2,3,4];

let b = a.map((item)=>{
	return item*2;
})

console.log(b);//[2,4,6,8]

shift

返回并删除数组中的第一个元素

let a = [1,2,3,4];

console.log(a.shift());//1

console.log(a);//[2,3,4]

toString

把一个数组转为字符串，并以逗号分割

let a = [1,2,3,4];

console.log(a.toString());//1,2,3,4

splice

用于向数组中添加或删除元素

//index为要添加或删除元素的起始位置
// howmany为要删除的数量 必须为数字，可以为0 ，未传此参数会删除起始位置一直到结束的元素
// item为要添加的元素
arr.splice(index,howmany,item,...,item)

从索引0开始删除一个元素，并返回被删除的元素

//例如
let a = [1,2,3];
//
console.log(a.splice(0,1));//[1]

console.log(a);//[2,3]

从索引1开始，删除一个元素，并添加两个元素

let a = [1,2,3];

console.log(a.splice(1,1,5,6));//[2]

console.log(a);//[1,5,6,3]