flat

function flat(arr = [1,2,3,[4,5,[6,7]]],deep = 0){
    if(deep <= 0){
        return arr
    }
    if(deep == Number.Infinity){
        while(arr.some(Array.isArray)){
            arr = [].concat(...arr)
        }
        return arr
    }
    while(arr.some(Array.isArray) && deep > 0){
        arr = [].concat(...arr)
        deep--
    }
    return arr
}