The Correct Way to Clone Javascript Arrays

So what you're really asking is there an easy way to do a deep copy. And the answer to that is "no." (Sadly, the answer to "is there a good way to do a deep copy" is also "no" if you ever include any DOM objects.)

However, an array of objects can be cloned. Just remember that it's really an array of object references, and you're creating a copy of the array of object references.

Otherwise, your best bet for a deep copy is:

function deepCopy(obj) {
  if (typeof obj == 'object') {
    if (isArray(obj)) {
      var l = obj.length;
      var r = new Array(l);
      for (var i = 0; i < l; i++) {
        r[i] = deepCopy(obj[i]);
      }
      return r;
    } else {
      var r = {};
      r.prototype = obj.prototype;
      for (var k in obj) {
        r[k] = deepCopy(obj[k]);
      }
      return r;
    }
  }
  return obj;
}

var ARRAY_PROPS = {
  length: 'number',
  sort: 'function',
  slice: 'function',
  splice: 'function'
};

/**
 * Determining if something is an array in JavaScript
 * is error-prone at best.
 */
function isArray(obj) {
  if (obj instanceof Array)
    return true;
  // Otherwise, guess:
  for (var k in ARRAY_PROPS) {
    if (!(k in obj && typeof obj[k] == ARRAY_PROPS[k]))
      return false;
  }
  return true;
}

Note that this will only really work on JSON objects. It sort of works on regular JavaScript objects solely because the functions from the prototype will show up in the iteration - but the cloned object won't be an "instanceof" object.

There's no real way around that because there's no JavaScript-standard way of getting the prototype from the original object.