JS code the generates random array of numbers and sort it using merge sort without using recursive function call

Merge Sort without recursion

// Inspired by the game 2048 :D

function merge(left, right) {
	var result = [];
	while(left.length || right.length) {
	  if(left.length && right.length) {
	    if(left[0]<right[0]) {
	      result.push(left.shift());
	    } else {
	      result.push(right.shift());
	    }
	  } else if (left.length) {
	    result.push(left.shift());
	  } else {
	    result.push(right.shift());
	  }
	}
	return result;
}

function generateRandomList(num){
	var gen = {};
	var arr = [];
	var base = parseInt("10" + Array(num.toString().length).join("0"));
	var num = parseInt(num);
	for(n=0;Object.keys(gen).length<num;n++){
		rand = parseInt(Math.random()*base);
		if(gen[rand]==undefined){
			gen[rand] = "";
			arr.push(rand);
		}
	}
	function comparator(left, right) {
		if (left > right) return 1
		else if (left < right) return -1
		else if (left == right) return 0
	}
	return arr;
}

var originalArray = generateRandomList(100);


loopSize = originalArray.length/2;
stack = [];
for(n=0;n<loopSize;n++){
	var aIdx = n*2 ;
	left = originalArray.slice(aIdx,aIdx+1);
	aIdx++;
	right = originalArray.slice(aIdx,aIdx+1);
	merged = merge(left,right);
	stack.push(merged);
	
	while(stack.length>=2){
		if(stack[stack.length-1].length==stack[stack.length-2].length){
			left = stack.pop();
			right = stack.pop();
			stack.push(merge(left,right));
		}else{
			break;
		}
	}
}

while(stack.length>=2){
		left = stack.pop();
		right = stack.pop();
		stack.push(merge(left,right));
}


console.log(JSON.stringify(stack[0]))