The Tor Browser / file revision

 // test whether splice works on arguments

 function splice_args () {

     args = arguments;

     return Array.prototype.splice.apply(args, [0, 5]);

 }

 var args;

 var O = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];

 var A = splice_args.apply(undefined, O)

 // args: [5, 6, 7, 8, 9]

 assertEq(args[0], 5);

 assertEq(args[1], 6);

 assertEq(args[2], 7);

 assertEq(args[3], 8);

 assertEq(args[4], 9);

 assertEq(args.length, 5);

 // A: [0, 1, 2, 3, 4]

 assertEq(A[0], 0);

 assertEq(A[1], 1);

 assertEq(A[2], 2);

 assertEq(A[3], 3);

 assertEq(A[4], 4);

 assertEq(A.length, 5);

 // O: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

 assertEq(O[0], 0);

 assertEq(O[1], 1);

 assertEq(O[2], 2);

 assertEq(O[3], 3);

 assertEq(O[4], 4);

 assertEq(O[5], 5);

 assertEq(O[6], 6);

 assertEq(O[7], 7);

 assertEq(O[8], 8);

 assertEq(O[9], 9);

 assertEq(O.length, 10);