Edit in JSFiddle

var fibonacci = function()
{
	var memo = [];
  
  var fiboFunc = function(num){
  var result;
 	if(num in memo)
  {
  	return memo[num];
  }
  else
  {
  	if(num==0 || num==1)
  {
  	memo[num] = num;
  	return num;
  }
  else
  {
  	result = fiboFunc(num-1)+fiboFunc(num-2);
  	memo[num] = result;
  	return result;
  }
  
  }
	
  };
  
  return fiboFunc;
  
}
var fibo = new fibonacci()
console.log(fibo(5));
console.log(fibo(7))