Classes

Defining classes

defineClass receives a class prototype and creates a generated a class. The special constructor method is treated as a class constructor;

var Device = defineClass({
    constructor: function (ram) {
        this.ram = ram;
    },

    turnOn: function () {
        console.log("Turning on...");
    }
});

var device = new Device(1000);
device.turnOn(); // Turning on
assert(device instanceof Device);

Default field values

If a field has an immutable default value, it can be included in the prototype.

var Device = defineClass({

    // define a default variable name
    hasBattery: false,

    constructor: function (ram) {
        this.ram = ram;
    },

    turnOn: function () {
        console.log("Turning on...");
    }
});

var device = new Device(1000);
assert(device.hasBattery === false);

Constructor is optional

Here is the minimal class definition:

var MinimalClass = defineClass({});

Inheritance

A special _super field in a prototype is reserved for inheritance and can reference a base class.

A subclass inherits the members of its base class. It is not required to re-define the constructor in a prototype.

var Phone = defineClass({

    // specify the base class
    _super: Device,

    // define a new method
    dial: function (number) {
        console.log("Dialing to " + number);
    }
});

var phone = new Phone(1000); // base constructor is called
phone.dial("120-0000"); // Output: Dialing to 120-0000
assert(phone instanceof Phone);
assert(phone instanceof Device);

Overriding methods and calling base methods

Members in a subclass override the base members of the same name. To call a base method, call the special this._super method. It applies to constructors too.

var Phone = defineClass({
    _super: Device,

    // override a constructor
    constructor: function (ram, number) {
        // you may have code before calling the base constructor
        this.number = number;
        // call the base contructor
        this._super(ram);
    },

    // override a method
    turnOn: function () {
        // call the base method
        this._super();
        console.log("Playing sound");
    },

    dial: function (number) {
        console.log("Dialing to " + number);
    }
});

var phone = new Phone(100, "120-1010");
phone.turnOn(); // Output: Turning on...\nPlaying sound
assert(phone.number === "120-1010");

The _super field value changes from method call to method call, so it may be used only in the method that has overridden the base method. Do not use it in a nested function unless you know what you are doing.

Overriding default field values

You can not only override methods but default field values as well.

var Phone = defineClass({
    _super: Device,
    hasBattery: true
});

var phone = new Phone(1000);
assert(phone.hasBattery);