Phaser Javascript 游戏、此关键字和游戏状态

Question

I have just started using Phaser to create Javascript games and have questions regarding the 'this' keyword.

• Does this refer to the current state (rainState)?

• I assume this.emitter = this.game.add.emitter(100, 0, 400); creates an emitter property on the rainState object that stores an emitter object ?

• Is game a property of state? why do write this.game.add.emitter as opposed to this.add emitter

//-------------------------------------------------

     var Smash = Smash || {};

    Smash.rainState = {
        create: function() {
            this.emitter = this.game.add.emitter(this.game.world.centerX, 0, 400);

            this.emitter.width = this.game.world.width;
            this.emitter.angle = 30;
            this.emitter.makeParticles('particle');

            this.player = new Smash.Player(this.game, 100, 300, 'player');

            this.intro0();       
        },

        intro0: function() {
          this.player.animations.play("run", 9, true);
        },
    };

Answer 1

Does this refer to the current state (rainState)?

The answer is it depends how it is called.

If it's called as a method of the rainState object, the context ( this ) will be set to the rainState object:

Smash.rainState.create();

Using call , apply , or bind you can pass in whatever scope you want as an argument:

Smash.rainState.create.call(foo); //immediately invoked
Smash.rainState.create.apply(foo); //immediately invoked
var bar = Smash.rainState.create.bind(foo); //reference to a newly created bound function

I assume this.emitter = this.game.add.emitter(100, 0, 400); creates an emitter property on the rainState objects that stores an emitter object ?

Yes when you assign a value to this.emitter it is added as a property of the object rainState .

Smash.rainState = {
    create: function() {
        console.log(Smash.rainState.emitter); //undefined
        this.emitter = this.game.add.emitter(this.game.world.centerX, 0, 400);
        console.log(Smash.rainState.emitter); //[object Object]
    },      
};

Is game a property of state? why do write this.game.add.emitter as opposed to this.add emitter

Based on the code you've provided, it doesn't look like game is a method or property of rainState . Furthermore, this.add is not a built-in function of the object type. Unless game has been added as a property of rainState somewhere else, you'll need to refer to it in another way.

Globally:

var game = new Phaser.Game();

var Smash = Smash || {};

Smash.rainState = {
    create: function() {
         this.emitter = game.add.emitter(this.game.world.centerX, 0, 400);

As a parameter passed in from a place where game exists in context:

Smash.rainState = {
    create: function(game) {
         this.emitter = game.add.emitter(this.game.world.centerX, 0, 400);
    }
}

//a context where game is a property
{
    this.game = new Phaser.Game();   

    Smash.rainState.create(this.game);
}

Phaser has some specific settings around how you refer to the game instantiation of the Phaser.Game class in different contexts:

"Via": If a class has an entry in the via column it means you can quickly access it through a local reference. Ie you can control the camera via this.camera from any state, or game.camera if game has been globally defined.

This means if you initialized your game instance in the global scope (outside of any {} ) then you should be able to call it globally. Look for something like this in your code and make sure it's not inside another function or object:

var game = new Phaser.Game(800, 600, Phaser.AUTO, 'phaser-example', { preload: preload, create: create, update: update, render: render });