How to copy or duplicate an array of arrays

Question

I'm trying to make a function that duplicates an array of arrays. I tried blah.slice(0); but it only copies the references. I need to make a duplicate that leaves the original intact.

I found this prototype method at http://my.opera.com/GreyWyvern/blog/show.dml/1725165

Object.prototype.clone = function() {
  var newObj = (this instanceof Array) ? [] : {};
  for (i in this) {
    if (i == 'clone') continue;
    if (this[i] && typeof this[i] == "object") {
      newObj[i] = this[i].clone();
    } else newObj[i] = this[i]
  } return newObj;
};

It works, but messes up a jQuery plugin I'm using - so I need to turn it onto a function... and recursion isn't my strongest.

Your help would be appreciated!

Cheers,

Be sure to declare "i" with `var`! Also it's risky to iterate over an array with a `for ... in` loop - much safer to use numeric indexes. — Pointy, Feb 22 '12 at 17:02
See: http://stackoverflow.com/questions/565430/deep-copying-an-array-using-jquery — Diodeus - James MacFarlane, Feb 22 '12 at 17:04

score 5 · Accepted Answer · answered Feb 22 '12 at 17:04

function clone (existingArray) {
   var newObj = (existingArray instanceof Array) ? [] : {};
   for (i in existingArray) {
      if (i == 'clone') continue;
      if (existingArray[i] && typeof existingArray[i] == "object") {
         newObj[i] = clone(existingArray[i]);
      } else {
         newObj[i] = existingArray[i]
      }
   }
   return newObj;
}

georg · Answer 2 · 2012-02-22T17:16:15.130

2

For example:

clone = function(obj) {
    if (!obj || typeof obj != "object")
        return obj;
    var isAry = Object.prototype.toString.call(obj).toLowerCase() == '[object array]';
    var o = isAry ? [] : {};
    for (var p in obj)
        o[p] = clone(obj[p]);
    return o;
}

improved as per comments

edited Feb 22 '12 at 17:16

answered Feb 22 '12 at 17:04

georg

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Will break for `null` (null.pop will throw). The first check should be something like `if (typeof obj != "object" || !obj)`. – Alexander Pavlov Feb 22 '12 at 17:06
Also, questionable handling of inherited properties - "clone" in JavaScript has problematic semantics. – Pointy Feb 22 '12 at 17:07

How to copy or duplicate an array of arrays

2 Answers2