Question

I have this code, wich adds Node to array and then changes it, the firstNode object is set in the init function.

var myClass = function() {
    this.items = []
    this.firstNodeValues = {};

    this.init = function() {
        var firstIndex = false;

        for (i = 10; i <= 15; i++) {
            Node = {};
            Node.index = i;
            Node.name = "undefined";
            if (i == 10) {
                Node.name = "John"
                this.firstNodeValues = Node;
            }
            this.items[i] = Node;
        }
    }

    this.iterate = function() {
        var newIndex = 10;
        for (i = 10; i <= 15; i++) {
            this.items[i].index = newIndex;
            if (i == 10) {
                this.items[i].name = "Michael";
            }
            newIndex++;
        }
    }
}
var test = new myClass();
test.init();
console.debug(test.firstNodeValues.name) // this gives value "John"
test.iterate();
console.debug(test.firstNodeValues.name) // this gives value "Michael"

The second debug returns "Michael" but why? It looks the firstNodeValues has a pointer to the node items[10].
I want that if I set the FirstNodeValues in firstTime and later a change Node values then the firstNodeValues is not Changes and stay exactly the same as I first set it.

Answer 1

The reason your clone is changing when you change your data is this:

this.firstNodeValues = Node;

There, you are declaring firstNodeValues to be a reference to Node, not a copy. So everything you change in firstNodeValues, changes in Node, and vice versa.

You’ll need to clone the object, like this:

function clone(obj){
    if(obj == null || typeof(obj) != 'object'){
        return obj;
    }

    var temp = {};

    for(var key in obj){
        if(obj.hasOwnProperty(key))){
            temp[key] = clone(obj[key]);
        }
    }
    return temp;
}

Then, you can copy the node, like this:

this.firstNodeValues = clone(Node);

This will make sure that this.firstNodeValues isn’t a reference to Node, but a new object, with the same properties / values as Node (So, a clone).