JS getters and setters inside a class?

Question

I'd like to create a class in JS that uses native getters and setters. I know I can create getters/setters for objects, like so:

var obj = {
    get value(){
        return this._value;
    },
    set value(val){
        this._value = val;
    }
}

I also know that I can use this.__defineGetter__ inside a class/function, but MDN says that using __defineGetter__() etc is discauraged.

Is there any better way to add getters and setters to js class than:

function class(){
};

class.prototype = {
   get value(){
        //....

}

?

Answer 1

2019: Hooray for ES6!

class Person {
    
    get name() {
        return this._name + '!!!'
    }

    set name(newValue) {
        this._name = newValue
    }

    constructor(name) {
        this._name = name
    }
}

const me = new Person('Zach')
console.log(me.name)            // Zach!!!

me.name = 'Jacob'
console.log(me.name)            // Jacob!!!

// Of course, _name is not actually private.
console.log(me._name)           // Jacob

Answer 2

The cleanest way to define properties on a class is via Object.defineProperties. This allows you to define all of your properties in a single, easily readable block. Here's an example:

var MyClass = function() {
    this._a = undefined;
    this._b = undefined;
};

Object.defineProperties(MyClass.prototype, {
    //Create a read-only property
    a : {
        get : function() {
            return this._a;
        }
    },
    //Create a simple read-write property
    b : {
        get : function() {
            return this._b;
        },
        set : function(value) {
            this._b = value;
        }
    }
});

There are a plethora of other options when defining properties, so be sure to check out the link I posted for more information. It's also important to keep in mind that even the most basic getter/setter property is only as fast as a method call in current browsers, so they can become a bottleneck in performance-intensive situation.