Variable not changing when function is called

Question

Anyone see a bug in my code that stops the variable "player1Bananas" from changing? Everything else in the function works fine.

 //update playerStats arguments:
    //banana is a banana object
    //x and y are the banana's position
    //players bananas is player1Bananas or player2Bananas,
    //ballPosition is "left" or "right"
    updatePlayerStats: function(banana, x, y, playersBananas, ballPosition) {   
        playersBananas += 1;
        gameController.bananasTaken += 1;
        banana.x = x;
        banana.y = y;
        gameController.player1Score = 0;
        gameController.player2Score = 0;
        gameController.setUpPaddles();
        gameController.setUpBall(ballPosition);
    },
    gameController.updatePlayerStats( gameController.Banana1, 20, gameController.canvas.height - 20 - gameController.Banana1.height,
 gameController.player1Bananas, "left");

Thanks!

Cause function get it by-value. read: http://stackoverflow.com/questions/6605640/javascript-by-reference-vs-by-value — Ivan Chernykh, Jul 30 '13 at 06:49
I recommend you create accessor functions to abstract some of your code. You can simply call `gameController.giveBanana()` which will increase the `bananasTaken` and increase `playersBananas`. It will help you later if you ever change the variable name or make any other changes. — Jared, Jul 30 '13 at 07:00

Jared · Answer 1 · 2013-07-30T06:57:37.110

5

You're passing the value of gameController.player1bananas as a parameter to a function.

In the function that value is assigned to local variable playersBananas and is restricted by scope. When you make a change to it, you're no longer making a change to that variable you originally passed but instead the new variable playersBananas.

Example: http://jsfiddle.net/GHkJ6/

To fix this, you need to pass it as an object. JavaScript won't pass it as a value, but instead the object itself.

Example: http://jsfiddle.net/F446Q/

edited Jul 30 '13 at 06:57

answered Jul 30 '13 at 06:51

Jared

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Thanks i'm doing that now – user2602079 Jul 30 '13 at 07:08

score 2 · Answer 2 · answered Jul 30 '13 at 06:49

2

Because in JavaScript numbers are passed by value...

You have to pass something else than a single number, like a player state object({id:1, bananas:17} for example).

answered Jul 30 '13 at 06:49

Mmmh mmh

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score 1 · Accepted Answer · answered Jul 30 '13 at 06:56

gameController.player1Bananas is a primitive type, so it is passed by value... not reference. This means that inside the function playerBananas no longer has any reference to player1Bananas, it is simply an integer value.

Try passing in an object instead... for example, you could have a player object with a bananaCount property. Then pass the player object into the function and increment the bananaCount property of the player object.

eg.

 //update playerStats arguments:
    //banana is a banana object
    //x and y are the banana's position
    //players bananas is player1Bananas or player2Bananas,
    //ballPosition is "left" or "right"
    updatePlayerStats: function(banana, x, y, player, ballPosition) {   
        player.bananaCount += 1;
        gameController.bananasTaken += 1;
        banana.x = x;
        banana.y = y;
        gameController.player1Score = 0;
        gameController.player2Score = 0;
        gameController.setUpPaddles();
        gameController.setUpBall(ballPosition);
    },
    gameController.updatePlayerStats( gameController.Banana1, 20, gameController.canvas.height - 20 - gameController.Banana1.height,
 gameController.player1, "left");

See this link for a good explanation.. http://snook.ca/archives/javascript/javascript_pass

Thanks, i think this solution is the best way to go for my game. — user2602079, Jul 30 '13 at 07:13

score 0 · Answer 4 · answered Jul 30 '13 at 06:54

0

change player1Bananas to global variable then change that same player1Bananas inside the function

answered Jul 30 '13 at 06:54

Variable not changing when function is called

4 Answers4