Question

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.

Thoughts?

Answer 1

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.