get difference between two arrays (including duplicates)

Question

I see a lot of posts about how to get the difference and symmetric difference of an array in javascript, but I haven\'t found anything on how to find the difference, includi

Answer 1

So, I'd:

• Iterate the updated array, for each element check if it's present on original array, if it's present I remove it from original array (note: in the function below I copy the original object, so I don't affect it), else I push the element to the differences array. At the end, I return the differences array.

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This code is made to work on various browsers, thus I didn't use Array().indexOf and other newer methods of ECMAScript.

function difference(updated, original) {
  var i, l;
  /* copy original array */
  var degradation = [];
  for (var i = 0, ol = original.length; i < ol; ++i)
    degradation[i] = original[i]

  var diff = [];
  for (i = 0, l = Math.max(updated.length, ol); i < l; ++i) {
    var upd = updated[i];
    var index;
    var b, found;
    /* find updated item in degradation */
    for (b = 0, found = false; b < ol; ++b) {
      if (degradation[b] === upd) {
        /* remove item from degradation */
        delete degradation[b];
        found = true;
        break;
      }
    }
    if (!found)
      diff.push(upd);
  }
  return diff;
}