Programmatically control breakpoints in Javascript?

You can use debugger; in code to make breakpoint for firebug. For example:

alert('1');
debugger;
alert('2');

And firebug automatically stops on this keyword.

First you could add a call to a function like __checkDebug(); which will check for a global (or semi-global) variable and when said variable is true, call debugger.

  
function __checkDebug() {
   if (debugme) debugger;
}

all of your functions you're concerned about debugging would be like so:

  
function foo() {
   __checkDebug();

   //.... whatever foo was gonna do.
}

You can then take it a little further and dynamically decorate functions while the code is being executed like so:

Function.prototype.debug = function(){   
   var fn = this; 
   return function(){     
       if (debugme) debugger; 
       return fn.apply(this, arguments);     
   }; 
}; 

foo = foo.debug();  

now any time foo is called it will call debugger if the debugme variable is truthy.

Another option would be to build a javascript build system that injects the call after every function declaration - this requires a syntax parser but if you're only looking to modify functions a simple tokenizer for that use case is pretty easy to write - but I'll leave that up to you.

Have a look at the FireBug functions debug(fn) & undebug(fn) names which set a breakpoint on the first line of the named function.

See point #6:

http://michaelsync.net/2007/09/30/firebug-tutorial-script-tab-javascript-debugging