The Tor Browser / file revision

 // Basic breakpoint test.

 var g = newGlobal();

 g.s = '';

 var handler = {

     hit: function (frame) {

         assertEq(this, handler);

         g.s += '1';

     }

 };

 var dbg = Debugger(g);

 dbg.onDebuggerStatement = function (frame) {

     g.s += '0';

     var line0 = frame.script.getOffsetLine(frame.offset);

     var offs = frame.script.getLineOffsets(line0 + 2);

     for (var i = 0; i < offs.length; i++)

         frame.script.setBreakpoint(offs[i], handler);

 };

 g.eval("debugger;\n" +

        "s += 'a';\n" +  // line0 + 1

        "s += 'b';\n");  // line0 + 2

 assertEq(g.s, "0a1b");