The Tor Browser / file revision

 // A breakpoint handler may clear itself.

 var g = newGlobal();

 var bphits = 0;

 var handler = {hit: function (frame) { frame.script.clearBreakpoint(this); bphits++; }};

 var dbg = Debugger(g);

 var hits = 0;

 dbg.onDebuggerStatement = function (frame) {

     var offs = frame.script.getLineOffsets(g.line0 + 3);

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

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

     hits++;

 };

 g.eval("var line0 = Error().lineNumber;\n" +

        "debugger;\n" +                    // line0 + 1

        "for (var i = 0; i < 4; i++)\n" +  // line0 + 2

        "    result = 'ok';\n");           // line0 + 3

 assertEq(hits, 1);

 assertEq(bphits, 1);