flat

Array.prototype.myFlat = function(deep = 1){
    let arr = this
    if(deep == Number.Infinity){
        while(arr.some(Array.isArray)){
            arr = [].concat(...arr)
        }
        return arr
    }
    while(arr.some(Array.isArray) && deep > 0 && Number.isInteger(deep)){
        arr = [].concat(...arr)
        deep--
    }
    return arr
}