JS defineProperty and prototype

Question

As you know we can define getters and setters in JS using defineProperty(). I\'ve been stuck when trying to extend my class using defineProperty().

Answer 1

This solution is without extra memory consumption. Your updated code is close. You just need to use this.props[field_name] instead of direct this[field_name].

Please note that defineProperty call replaced to Object.create

Js Fiddle http://jsfiddle.net/amuzalevskyi/65hnpad8/

// util
function createFieldDeclaration(fields) {
    var decl = {};
    for (var i = 0; i < fields.length; i++) {
        (function(fieldName) {
            decl[fieldName] = {
                get: function () {
                    return this.props[fieldName];
                },
                set: function (value) {
                    this.props[fieldName] = value;
                }
            }
        })(fields[i]);
    }
    return decl;
}

// class definition
function User(id, name) {
    this.props = {};
    this.id = id;
    this.name = name;
}
User.prototype = Object.create(Object.prototype, createFieldDeclaration(['id','name']));

// tests
var Alex = new User(0, 'Alex'),
    Andrey = new User(1, 'Andrey');

document.write(Alex.name + '
'); // Alex
document.write(Andrey.name + '
'); // Andrey

Alex.name = "Alexander";
document.write(Alex.name + '
'); // Alexander
document.write(Andrey.name + '
'); //Andrey