编辑代码

let arr=[1,2,3,[[4,5],6],7,8,9];
// 1.递归
function flattern(arr) {
    let result=[];
    for(let i=0;i<arr.length;++i) {
        if(Array.isArray(arr[i])) {
            result=result.concat(flattern(arr[i]));
        }else {
            result=result.concat(arr[i]);
        }
    }
    return result;
}
console.log(flattern(arr));
// 2.toString()
let p=arr.toString().split(",").map((item)=>Number(item));
console.log(p);
arr.flat(Infinity);