Reimplementation for unshift in JS

unshift.js

let  deepCopy =  function(copied, copy){
  let i = 0, len = copy.length;

  for(i; i < len; i++){
    copied[i] = copy[i]
  }

  return copied;
}

Array.prototype.unShift  = function (){
  let newArray  = [...arguments], i = 0, len  =  this.length, newArrLen =  newArray.length;
  for(i; i < len; i++,newArrLen++){
    newArray[newArrLen] = this[i];
  }

  deepCopy(this, newArray);
}


//Another unshift implementation without deep copy 
Array.prototype.unShift  = function (first){
  let len  =  this.length, i = len;

  for(i; i > 0; i--){
     this[i] = this[i - 1];
  }
  
  this[0] =  first;
}


let arr =[1,2];
arr.unShift(3);
arr // [3,1,2]