A first Debugging Session with Firebug


During my last development I hit the following problem :

  • My Slider application does not start with the following error
  • Something goes wrong here but without a Stack Trace debugging is annoying


Start Debugging Firebug [ by pressing F12 – Firebug should be already installed ]

  • Preselect our source slider.js within Firebug


Set a breakpoint in function checkTrackIndex()

  • Right click and set the breakpoint at the line where the error condition is handled
  • After setting a breakpoint  press F8 to continue or you may need to reload your page



Restart the application and check out the status


  • The application stops at line 1247 in function checkTrackIndex()
  • Lets see what detail info is available by pressing the Stack tab


  • Now we should have a better understanding  what is going on
  • checkTrackInfoLoadStatus() calls loadroute() which calls checkTrackIndex()
  • In checkTrackIndex() lidx is undefined – Why ?
  • press on the loadRoute() function for further investigations


  •  At line 2737 we can see that checkTrackIndex() is called without a variable
  • This explains why the lidx variable in checkTrackIndex()  is undefined 


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