The Tor Browser / file revision

 // Clearing a breakpoint by handler can clear multiple breakpoints.

 var g = newGlobal();

 var dbg = Debugger(g);

 var s;

 dbg.onDebuggerStatement = function (frame) {

     s = frame.eval("f").return.script;

 };

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

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

        "    return a + b;\n" +      // line0 + 2

        "}\n" +

        "debugger;\n");

 var hits = 0;

 var handler = {hit: function (frame) { hits++; s.clearBreakpoint(handler); }};

 var offs = s.getLineOffsets(g.line0 + 2);

 for (var i = 0; i < 4; i++) {

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

         s.setBreakpoint(offs[j], handler);

 }

 assertEq(g.f(2, 2), 4);

 assertEq(hits, 1);

 assertEq(s.getBreakpoints().length, 0);