JavaScript constructor and melonJS questions

Question

I'm following this MelonJS tutorial. I'm getting familiar with OOP- classes, constructors, etc... I have some questions about constructors.

In the following code snippet...

1) is init a melonJS special function (I read thru API, http://melonjs.github.io/docs/me.ObjectEntity.html, doesn't seem to be melon), or JavaScript? It seems to be called automatically when the playerEntity is created... what is calling init?

2) It seems sometimes this is called (this.setVelocity), sometimes me is called (me.game.viewport.follow). When do you call each?

3) For velocity, why do you need to multiply accel * timer tick? : this.vel.x -= this.accel.x * me.timer.tick;

    /*------------------- 
a player entity
-------------------------------- */
game.PlayerEntity = me.ObjectEntity.extend({

    /* -----

    constructor

    ------ */

    init: function(x, y, settings) {
        // call the constructor
        this.parent(x, y, settings);

        // set the default horizontal & vertical speed (accel vector)
        this.setVelocity(3, 15);

        // set the display to follow our position on both axis
        me.game.viewport.follow(this.pos, me.game.viewport.AXIS.BOTH);

    },

    /* -----

    update the player pos

    ------ */
    update: function() {

        if (me.input.isKeyPressed('left')) {
            // flip the sprite on horizontal axis
            this.flipX(true);
            // update the entity velocity
            this.vel.x -= this.accel.x * me.timer.tick;
        } else if (me.input.isKeyPressed('right')) {

Answer 1

init is a constructor - every object that is created with the Object.extend() method will implement an interface that defines an init method.

As for the this vs. me - see the documentation:

• me refers to the melonJS game engine - so all melonJS functions are defined in the me namespace.

• this is going to refer to whatever this is in the given context. For example, in your code snippet provided, it would refer to the instance of the player entity.