Sean Thoman Sean Thoman - 3 months ago 31
Javascript Question

Immutable types in javascript

It seems to me that immutable types are impossible in Javascript, or does anyone know of any tricks to create them? Is it a good or bad practice?

For instance something like,

var Point2D = function Point2D(x, y) {

var _x = x;
var _y = y;

function constructor() {

var self = {};

// Pseudo-Immutable concept
self.x = function() {
return _x;

self.y = function() {
return _y;

return self;

return constructor();


Which of course isn't really immutable, but if it were either 1) well-documented that the properties 'x' and 'y' are getter-functions or 2) threw some kind of alert when validating for immutability then it could act as a de-facto immutable object.



If you don't have to worry about older browsers you can look into Object.defineProperty.

Other than that, I don't think there is much of an option since any function/property on an object can be redefined at any point in JavaScript.