The Tor Browser / file revision

 // Map methods throw when passed a this-value that isn't a Map.

 load(libdir + "asserts.js");

 function testcase(obj, fn) {

     assertEq(typeof fn, "function");

     var args = Array.slice(arguments, 2);

     assertThrowsInstanceOf(function () { fn.apply(obj, args); }, TypeError);

 }

 var Map_size_getter = Object.getOwnPropertyDescriptor(Map.prototype, "size").get;

 function test(obj) {

     testcase(obj, Map.prototype.get, "x");

     testcase(obj, Map.prototype.has, "x");

     testcase(obj, Map.prototype.set, "x", 1);

     testcase(obj, Map.prototype.delete, "x");

     testcase(obj, Map.prototype.clear);

     testcase(obj, Map.prototype.keys);

     testcase(obj, Map.prototype.values);

     testcase(obj, Map.prototype.entries);

     testcase(obj, Map_size_getter);

 }

 test(Map.prototype);

 test(Object.create(new Map));

 test(new Set());

 test({});

 test(null);

 test(undefined);