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 // Array.of calls a "length" setter if one is present.

 var hits = 0;

 var lastObj = null, lastVal = undefined;

 function setter(v) {

     hits++;

     lastObj = this;

     lastVal = v;

 }

 // when the setter is on the new object

 function Pack() {

     Object.defineProperty(this, "length", {set: setter});

 }

 Pack.of = Array.of;

 var pack = Pack.of("wolves", "cards", "cigarettes", "lies");

 assertEq(lastObj, pack);

 assertEq(lastVal, 4);

 // when the setter is on the new object's prototype

 function Bevy() {}

 Object.defineProperty(Bevy.prototype, "length", {set: setter});

 Bevy.of = Array.of;

 var bevy = Bevy.of("quail");

 assertEq(lastObj, bevy);

 assertEq(lastVal, 1);