The Tor Browser / file revision

 // Hitting a breakpoint with no hit method does nothing.

 var g = newGlobal();

 g.s = '';

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

        "function f() {\n" +   // line0 + 1

        "    debugger;\n" +  // line0 + 2

        "    s += 'x';\n" +  // line0 + 3

        "}\n")

 var dbg = Debugger(g);

 var bp = [];

 dbg.onDebuggerStatement = function (frame) {

     g.s += 'D';

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

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

         var obj = {};

         bp[i] = obj;

         frame.script.setBreakpoint(arr[i], obj);

     }

 };

 g.f();

 assertEq(g.s, "Dx");

 dbg.onDebuggerStatement = undefined;

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

     bp[i].hit = function () { g.s += 'B'; };

 g.f();

 assertEq(g.s, "DxBx");