Untitled

Using temporary variables in a for loop
this.shuffle = function () {
    ...

this.leftHalf = this.cards.slice(0, this.size() / 2);
    this.rightHalf = this.cards.slice(this.size() / 2);
    this.result = [];

for (var i = ...) {
        this.result.unshift(this.leftHalf[i]);
        this.result.unshift(this.rightHalf[i]);
    }

this.cards = this.result;

    delete this.leftHalf;
    delete this.rightHalf;
    delete this.result;
}

var leftHalf, rightHalf, result;

this.shuffle = function () {
    leftHalf = ...

for(var i=...) {
   if(i%2 == 1)
      newdeck[i] = oldeck[N/2+(i-1)/2];
   if(i%2 == 0)
      newdeck[i] = oldeck[i/2];
}