Nodejs: how to clone an object

Question

If I clone an array, I use cloneArr = arr.slice()

I want to know how to clone an object in nodejs.

Answer 1

It's hard to do a generic but useful clone operation because what should be cloned recursively and what should be just copied depends on how the specific object is supposed to work.

Something that may be useful is

function clone(x)
{
    if (x === null || x === undefined)
        return x;
    if (typeof x.clone === "function")
        return x.clone();
    if (x.constructor == Array)
    {
        var r = [];
        for (var i=0,n=x.length; i

In this code the logic is

• in case of null or undefined just return the same (the special case is needed because it's an error to try to see if a clone method is present)
• does the object have a clone method ? then use that
• is the object an array ? then do a recursive cloning operation
• otherwise just return the same value

This clone function should allow implementing custom clone methods easily... for example

function Point(x, y)
{
    this.x = x;
    this.y = y;

    ...
}

Point.prototype.clone = function()
{
    return new Point(this.x, this.y);
};



function Polygon(points, style)
{
    this.points = points;
    this.style = style;

    ...
}

Polygon.prototype.clone = function()
{
    return new Polygon(clone(this.points),
                       this.style);
};

When in the object you know that a correct cloning operation for a specific array is just a shallow copy then you can call values.slice() instead of clone(values).

For example in the above code I am explicitly requiring that a cloning of a polygon object will clone the points, but will share the same style object. If I want to clone the style object too instead then I can just pass clone(this.style).