Phaser Functions with parameters in state issue

[KevinnFtw]

Hi guys,

 

 

Maybe a silly question, but I recently started using States in my game and now I am converting my functions to work with states.

 

The functions without parameters work fine, but the ones with parameters don't.

 

For example, when I call:

 

this.createBullet(x, y);

 

I get the error:

Uncaught typeError: undefined is not a function.

 

The function createBullet(x, y) does exist, it is created like this:

createBullet: function(x, y) {

      // blablabla content of function

}

 

p.s. these functions are in my Game.js state

 

Can anyone tell me what I'm doing wrong?

It has to be a silly mistake but I don't know how to fix it

 

 

Thanks,

Kevin

[Heppell08]

functions in states go:

fireBullet: function(){// stuff here}, // the comma is important too

[KevinnFtw]

Yeah I know that, but most of my functions need one or more parameters.

 

How should I handle them?

[Heppell08]

undefined issues mean if you have a firebullet function and are trying to instantiate it, you dont call fireBullet(); it is called with:

update: function(){fireBullet(); // without states this works, in states, nothis.fireBullet(); // this is for state like set ups.}

There should be no need for extra parameters, it must be the way you are calling the function. Use this.fireBullet(); [Example] instead of firebullet();

[Heppell08]

so if you have your player who fires a bullet, you would have::

if( ... keydown ... ){    this.fireBullet();}// orif(... keydown ...){ this.player.body.velocity.x = 250;}

[KevinnFtw]

I get that, but some of my functions need to have a couple of variables to work.

 

Normally, when I want to execute a certain function with parameters I would just call:

function(a);

 

I know that at states you have to use this.function if the function is inside of the game.

So then I would call this.function(a)

 

However when I do that I get the error

Uncaught typeError: undefined is not a function

 

The function(a) does exist.

 

Edit:

It might be that the context I'm using the function in is wrong, and not the function itself.

 

I'm using it within a socket.on like:

socket.on('newBullet', function(data) {

   this.function(data);

});

[rich]

Parameters aren't the cause of your problem I doubt, much more likely a scope issue. You need to show some actual code, it's hard to guess from posts alone. But the following is plucked from a game I'm working on (and abstracted down heavily to make it clear), may have some pointers:

TimesOfLores.Game = function (game) {    this.game = game;    this.map;    this.player;};TimesOfLores.Game.prototype = {    create: function () {        this.map = new TimesOfLores.Map(this);        this.player = new TimesOfLores.Player(this);        TimesOfLores.cursors.up.onDown.add(this.moveForward, this);    },    moveForward: function () {        this.checkExit(this.player.x, this.player.y);    },    checkExit: function (x, y) {        if (this.map.canPass(x, y))        {             this.player.moveForward();        }    }};

[KevinnFtw]

I've uploaded the Game.js here: http://jsbin.com/senarewe/1 

 

The problem is occuring at the createBullet() and createPlayer() functions.

[lewster32]

	    socket.on('newBullet', function(data) {	    	this.createBullet(data);	    });

Your 'this' reference within the anonymous function refers to itself, not the scope outside of the socket callback. Generally the way around this is to do 'var self = this;' within the correct scope, and then call 'self.createBullet(data);' instead.

            var self = this; // ensure 'self' is the desired context, as 'this' will change depending on where you call it	    socket.on('newBullet', function(data) {	    	self.createBullet(data);	    });

[KevinnFtw]

Ahh, i was thinking about the 'this' reference, but didn't know what to replace it with.

Edit: Awesome, it is working now! Thanks alot Rich and Lewster32 :-)

[lewster32]

You can call it anything, I tend to use 'self' but '_this' or 'that' are other common replacements. I tend to put 'var self = this;' at the top of my functions so that I can access that scope from inside the many anonymous functions I tend to end up using. Handily, Phaser's signals allow you to specify a context so it's not necessary for those, e.g.

this.game.time.events.add(1000, function() {  this.game.whatever(); // this.game is still accessible because...}, this); // ... the last parameter specifies the scope of the anonymous function

[rich]

Scope. The bane of JS devs worldwide

[lewster32]

Scope is easy, reliance on 'this' being whatever you want it to be - via witchcraft - is the true bane