Javascript Cloning

clone.js

// FROM http://stackoverflow.com/questions/728360/most-elegant-way-to-clone-a-javascript-object

// When I had to implement general deep copying I ended up compromising by 
// assuming that I would only need to copy a plain Object, Array, Date, String,
// Number, or Boolean. The last 3 types are immutable, so I could perform a 
// shallow copy and not worry about it changing. I further assumed that any 
// elements contained in Object or Array would also be one of the 6 simple 
// types in that list. This can be accomplished with code like the following:

function clone(obj) {
    // Handle the 3 simple types, and null or undefined
    if (null == obj || "object" != typeof obj) return obj;

    // Handle Date
    if (obj instanceof Date) {
        var copy = new Date();
        copy.setTime(obj.getTime());
        return copy;
    }

    // Handle Array
    if (obj instanceof Array) {
        var copy = [];
        for (var i = 0, len = obj.length; i < len; i++) {
            copy[i] = clone(obj[i]);
        }
        return copy;
    }

    // Handle Object
    if (obj instanceof Object) {
        var copy = {};
        for (var attr in obj) {
            if (obj.hasOwnProperty(attr)) copy[attr] = clone(obj[attr]);
        }
        return copy;
    }

    throw new Error("Unable to copy obj! Its type isn't supported.");
}

// The above function will work adequately for the 6 simple types I mentioned, 
// as long as the data in the objects and arrays form a tree structure. That
// is, there isn't more than one reference to the same data in the object. For 
// example:

// This would be cloneable:
var tree = {
    "left"  : { "left" : null, "right" : null, "data" : 3 },
    "right" : null,
    "data"  : 8
};

// This would kind-of work, but you would get 2 copies of the 
// inner node instead of 2 references to the same copy
var directedAcylicGraph = {
    "left"  : { "left" : null, "right" : null, "data" : 3 },
    "data"  : 8
};
directedAcyclicGraph["right"] = directedAcyclicGraph["left"];

// Cloning this would cause a stack overflow due to infinite recursion:
var cylicGraph = {
    "left"  : { "left" : null, "right" : null, "data" : 3 },
    "data"  : 8
};
cylicGraph["right"] = cylicGraph;