In javascript, if we copy objects or their properties, the reference still remains and by changing the new object the old one is changed, too. To clone or do a clean copy of an object I found a very useful solution by Jan Turoň on StackOverflow: Object.prototype.clone = function() { if(this.cloneNode) return this.cloneNode(true); var copy = this instanceof Array ? \[\] : {}; for(var attr in this) { if(typeof this\[attr\] == "function" || this\[attr\]==null || !