The Tor Browser / file revision

 /*

  * Any copyright is dedicated to the Public Domain.

  * http://creativecommons.org/licenses/publicdomain/

  */

 /* Create an object with a JavaScript setter. */

 var firstSetterCount;

 var o = { w:2, set x(v) { firstSetterCount++; } };

 /*

  * Put the object in dictionary mode, so that JSObject::putProperty will 

  * mutate its shapes instead of creating new ones.

  */

 delete o.w;

 /* A stock watcher function. */

 var watcherCount;

 function watcher(id, oldval, newval) { watcherCount++; return newval; }

 /*

  * Place a watchpoint on the property. The property's shape now has the

  * watchpoint setter, with the original setter saved in the watchpoint

  * structure.

  */

 o.watch('x', watcher);

 /*

  * Replace the setter with a new setter. The shape should get updated to

  * refer to the new setter, and then the watchpoint setter should be

  * re-established.

  */

 var secondSetterCount;

 Object.defineProperty(o, 'x', { set: function () { secondSetterCount++ } });

 /*

  * Assign to the property. This should trigger the watchpoint and the new setter.

  */

 watcherCount = firstSetterCount = secondSetterCount = 0;

 o.x = 3;

 assertEq(watcherCount, 1);

 assertEq(firstSetterCount, 0);

 assertEq(secondSetterCount, 1);

 reportCompare(true, true);