The Tor Browser / file revision

 function f1(a, bIs, cIs, dIs, b=a, c=d, d=5) {

     assertEq(a, 1);

     assertEq(b, bIs);

     assertEq(c, cIs);

     assertEq(d, dIs);

 }

 f1(1, 1, undefined, 5);

 f1(1, 42, undefined, 5, 42);

 f1(1, 42, 43, 5, 42, 43);

 f1(1, 42, 43, 44, 42, 43, 44);

 function f2(a=[]) { return a; }

 assertEq(f2() !== f2(), true);

 function f3(a=function () {}) { return a; }

 assertEq(f3() !== f3(), true);

 function f4(a=Date) { return a; }

 assertEq(f4(), Date);

 Date = 0;

 assertEq(f4(), 0);

 function f5(x=FAIL()) {};  // don't throw

 var n = 0;

 function f6(a=n++) {}

 assertEq(n, 0);

 function f7([a, b], A=a, B=b) {

     assertEq(A, a);

     assertEq(B, b);

 }

 f7([0, 1]);