二维数组降为一纬数组(数组扁平化)

1.join('').split(',')

let arr = [[1,2],[3,4]]
let newArr = arr.join('').spilt(',');
console.loh(newArr);// ['1','2','3','4']

2.reduce

let arr = [[1,2],[3,4]]
let newArr = arr.reduce(function (pre,cur){
	return pre.concat(cur)
})
console.log(newArr);// [1,2,3,4]

3.递归

let arr = [[1,2],[3,4]]
let newArr = [];
let toArr = (arr)=>{
	for(let i=0;i<arr.length;i++){
		if(arr[i] instanceof Array){
			toArr(arr[i])
		}else{
			newArr.push(arr[i])
		}
	}
}
toArr(arr);
console.log(newArr);// [1,2,3,4]

4.flat

// 默认参数是1, 也就是降一个数组, 取值为Infinity表示直接降维成一维数组
Array.flat();
let arr = [[1,2],[3,4]]
arr.flat();// [1,2,3,4]
let arr1 = [[1,2],[1,2,3,[4,5,6]]]
console.log(arr1.flat(Infinity));// 成一维数组

5.apply

let arr = [[1,2],[3,4]];
let newArr = [].concat.apply([],arr)
console.log(newArr)