Frequently Asked Questions

Troubles with the runtime

When I launch SlimerJS, nothing append, nothing is displayed in the console

Probably it is launched with an incompatible version of Firefox/XulRunner. If you use a lightweight edition, verify that the environment variable SLIMERJSLAUNCHER contains the path to a Firefox/XulRunner that is compatible with SlimerJS. To verify, launch /path/to/firefox --version or /path/to/xulrunner --version. The displayed version should be between MinVersion and MaxVersion indicated into the application.ini file of SlimerJS.

Sometimes SlimerJS hangs, it does not exit, the script is not totally executed

Verify that you have enough free memory on your system.

Rendering

The rendering of my web site is not really like in my favorite browser. Even in Firefox

A browser is very complex program. The final rendering (the appearance of the web page) depends on many different things:

• The browser engine (Gecko vs Webkit vs Presto vs Blink vs....).
• The version of the browser engine (improvements and bug fixes are made in each version of a browser).
• The library used to draw graphics: depending the operating system the browser is on, it uses a different graphics backend. For example, Firefox uses the Cairo library, which uses DirectX on windows, or other libraries on Linux or MacOs. So there are different algorithm, different implementations, to draw the same thing.
• The accelerated graphic cards: a browser can use hardware implementation or can use software implementations if the graphic cards has no accelerated graphic chipset. So different algorithm, different implementations: different results.
• To draw font (if the web page doesn’t use web fonts), it depends on the installed fonts
• Etc...

So, don’t expect to have exactly the same results between any browser and SlimerJS. Moreover, SlimerJS uses exactly the same rendering engine as Firefox: if you use the lighweight edition, it uses Firefox itself, and for other editions, it uses XulRunner, downloaded directly from Mozilla servers (and so built by Mozilla, exactly the same way they build Firefox). At least, the rendering with SlimerJs may be exactly the same as with Firefox (same gecko version, on the same operating system). However you could have some difference in some extrem case (high zooming for example) and with different operating system (even it is the same gecko version).

You can speak with us about rendering issues, on the mailing list.