No, it won't. This code:
function createThing() { return { doSomething: function(){} }; }
new Thing();
function doSomething(obj){} var objs = [{},{},{}]; objs.forEach(doSomething);
No, it won't. This code:
Performs much worse (at scale) than this code: And it consumes a lot more memory since Thing.prototype.doSomething is 1 function in memory and the former is N functions.