src/third_party/mozjs-45/js/src/jit-test/tests/debug/onDebuggerStatement-03.js

// A debugger statement in an onDebuggerStatement hook should not reenter.

var g = newGlobal();
var calls = 0;

var dbg = Debugger(g);
dbg.onDebuggerStatement = function (stack) {
    calls++;
    debugger;
};

assertEq(g.eval("debugger; 7;"), 7);
assertEq(calls, 1);