Question

I have a script setup like this (http://jsfiddle.net/YD66s/):

var countFull = new Array(0,1,2,3,4,5,6);
var countActive = new Array(0,1,2,3,4,5,6);

function pickRandom(a) {
  if(arguments[1].length == 0) {
      arguments[1] = arguments[0];
  }

  var m = Math.floor(Math.random()*arguments[1].length);
  chosen = arguments[1].splice(m,1);

  return chosen;
}

setInterval(function() {
  pickRandom(countFull,countActive);
}, 1000);

When I run this I want the variable to be set for that function only. Instead it is affecting countFull towards the end because I make arguments[1] = arguments[0]. How in javascript can I just reference a variable but not consume it and ultimately arguments[1] becomes arguments[0].

Hope this makes sense. This is driving me nuts how different javascript variables are compared to other languages like PHP.

Answer 1

Javascript arrays are just pointers so when you do arguments[1] = arguments[0] you actually just set the pointer but the underlying arrays are the same. As a result, every time you modify arguments[1] you also modify arguments[0]. To do what you want, you need to copy the array. You could do it this way:

if (arguments[1].length == 0) {
  for(var i = 0; i < arguments[0].length; i++) {
    arguments[1][i] = arguments[0][i];
  }
}