SOURCE

var arr = [{name: 'yy'}, [{name: 'gg'}, [{name: 'hh'},[{name:'lw'}]]], 1, 2]
console.log(arr.flat(3))

Array.prototype.myFlat = function(deep=1){
    let arr = this.slice();
    let flatArr = [];
    for(let i=0; i< arr.length; i++){
        if(Object.prototype.toString.call(arr[i]) === '[object Array]'){
            if(deep == 1){
                for(let j=0; j< arr[i].length; j++){
                    flatArr.push(arr[i][j])
                }
            }else {
                flatArr = flatArr.concat(arr[i].myFlat(deep-1))
            }
        }else {
            flatArr.push(arr[i])
        }
    }
    return flatArr;
}

console.log(arr.myFlat(1))
// console.log(arr)