Member functions & attributes

Objects can have behaviour and data, our Light object should have to ability to switch on and off. If someone would like to use our Light object they would switch it on using the on member function. To switch it off they will be using the off member function.

Member functions can be attached to a constructor function(Class) using the this keyword. The this keyword references the current instance of an object.

Use it like this:

var Light = function(color){
    this.color = color;
    var status = 'off';
    // create an `on` member function
    this.on = function(){
        status = 'on';
    }
    // create an `off` member function
    this.off = function(){
        status = 'off';
    }
}

Now you can switch a light on and off:

var greenLight = new Light('green');
//switch on the green light
greenLight.on();

You can switch a light on or off, but there are no way to see the status of the light. The status of the light is not visible from outside of the object as it is a private variable.

This will not work:

var greenLight = new Light('green');

//switch on the green light
greenLight.on();

// this will not work!!!
console.log(greenLight.status);