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Practical debugging

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This page gives you practical tips to debug your game during development. Don't hesitate to share your difficulties with us so that we can improve this section.


To work on BGA Studio, we recommend that you use Google Chrome as it's currently the fastest browser for the BGA platform, and it's available for all OSes.

Another reason to use Chrome is that it embeds all the tools you need to work on BGA Studio. You can see them by pressing "F12" or from the menu ("Tools > Development tools").

A good practice is to use a second browser to develop the game, in order to verify that your game is working fine on this browser too.

To debug with Firefox browser, we advise you to use these 2 extensions:

To debug with other browsers (IE, Edge, Opera), we advise you to use one of the most recent versions. Latest versions of the browser will likely have better development tools than the previous ones...

General tip for debugging

In general for debugging, think of using the 'save & restore state' functionality. It enables you to save the state of your game just before the issue you are investigating, then come back to that point with one click as many times as needed to understand what is going wrong.

You can save up to 3 different states.

Debugging my game when it cannot start

If your game won't start because of an error, you are probably in one of these situations:

  • There is a SQL error in your dbmodel.sql file.
  • You have a syntax error in your PHP file.
  • Your PHP "setup" - or any method used during the game initial states - generates an exception.

If the error is not explicitly displayed when you click on "Express start", you should check the "Gameserver error log" as per Studio logs. More cases of why game can't start are described on the Troubleshooting page.

Debugging my PHP game logic (or my view)

Most of the time, debugging PHP is quite easy. Here's what I do when I want to develop/debug some game logic that is triggered by some game action:

  • At first, I make sure that I can reproduce the needed game situation with one click. To do this, I use the "save & restore" function.
  • Another possibility for this is to place a die('ok'); PHP statement right after the PHP I am developing/debugging. This way, I make sure that every request will fail and then nothing will be committed to the database.
  • Then, I use the var_dump function to dump PHP variables and check what's wrong, until it works.


// ( code to debug)

var_dump( $my_variable );

// ( code to debug)

Add traces to your code

You can use the following functions in your game to add server side logging:

self::dump( 'name_of_variable', $variable ); // dump variable, like var_dump but in the log debug level logging, goes to BGA request&SQL logs

self::debug( $message ); // debug level logging, goes to BGA request&SQL logs

self::trace( $message ); // info level logging, goes to BGA request&SQL logs

self::warn( $message ); // warning level logging, goes to BGA unexpected exceptions log

self::error( $message ); // error level logging, goes to BGA unexpected exceptions log

Check Studio logs for more details on how to access your logs.

This can be useful when you need to follow the flow of your code and not just stop it to see how it goes at some point.

Only the error log level will appear in production. This level should be used only for critical problems. Other levels will show only in the development environment and can be used as you see fit.

Debugging my HTML/CSS layout

Example situations

  • Why doesn't my game element show up in the interface?
  • Why hasn't my CSS property been applied to this element?
  • Why is this game element displayed at this position?

A useful tip when an element does not show up in the interface is to give it a red background:

#my_element {
  ... some CSS definitions ...
  background-color: red;

This way, you know if the element is not visible because of some CSS property or because of something else.

Another tip: sometimes, changing a CSS property has no visible effect on your interface. In that case, add a "display:none" property. If your element does not disappear, the bug probably comes from your CSS selector and not from your CSS property.

Using Chrome "Elements" tab (the first one), you can:

  • See the CURRENT HTML of your page. Remember that the classical "show page source" is inefficient with BGA as you are modifying the page source with your Javascript code.
  • Using the "magnifying glass", you can click on any part of your game interface and check its HTML code and associated CSS styles.
  • You can even modify directly some CSS properties and see how it looks immediately in the game interface.

Debugging my Javascript game interface logic

Compared to PHP debugging, Javascript debugging can sometimes be painful.

Here are some tips to make your life easier while developing and debugging Javascript:

Do complex things on the PHP side

The most frequent case is the following: you want to compute possible moves in a game situation. Doing it in Javascript is a nightmare. Do it in PHP, and transfer the results to your client interface using the "args" game state property.

Note: See the Reversi tutorial for an example.

Add traces in your code

You can use the following:

console.log( variable_to_inspect )

It will give you the object structure of the variable in the Javascript console, without blocking the execution.

It's often a good idea to precede this call with a console.log( '### HERE ###' ); to find more easily the appropriate line in the console log.

alert( variable_to_inspect )

It will popup what you wish and pause the execution until you click ok.

This won't be useful for complex structures; only native types will be plainly displayed. But this is sometimes useful just with messages to make sure which way the execution goes.

Use Debugger

Modern browsers also allow you to put breakpoints in your js code.

This will stop code execution on that line and will launch the JavaScript debugger.

In Chrome, to add a breakpoint: add a line to your .js file


Refresh the page F5, and make sure you have the Developer tools window open, press F12. When the break-point is hit you can then step through your code and visualise variables, etc.

Online format checkers

Copy and paste code for a quick code sanity check like the right number of brackets.



Some frequent errors

See Troubleshooting.

Get the database matching a bug report

When a player creates a bug report in production, a snapshot of the game database is taken. You can get access to this snapshot from the studio by following the steps below:

  • Create a table in the studio with the same game and number of players as the table for which the report has been written. Launch this table.
  • Open another tab on the studio and go to "Manage game" page for your project (you have to be admin for this project)
  • In the "Errors in production" section, fill up the fields "Bug report ID" (this is the ID of the bug report in production) and "Studio table ID" (this is the ID of the table you created above) then click the "⇨ Load bug report state into this table save slot #1" button.
  • If the snapshot is correctly retrieved, you see a "Done!" message.
  • Go back to the tab with your studio table and click "Load 1".
  • The page refreshes automatically and is broken. This is normal, as the player ids from the snapshot are the player ids of the production, not those of the studio. We'll need to update them.
  • Click on the "Go to game database" button
  • For each table using player_ids, you'll need to update the player_ids from the production to use the player_ids from the studio. You can see the player_ids from the table page before entering the game by hovering over the player names.
  • Tables to update:
    • player
    • global (value with ID 2 is the active player)
    • stats
    • tables specific to your schema that use player_ids
  • If your changes to player_ids are not taken into account, it may be a cache problem: use the "Clear PHP cache" button on your "Manage game" page.
  • Then you should be able to play with the same state of the game as when the report was created in production.
  • If the game has ended, you can place it again in the game state you want to debug by setting the value with ID 1 in the global table to the appropriate state value, and the value with ID 2 to the player you want active).