javascript - Iterating through object's properties lists things in the prototype -

i'm trying make "copy" function , add object's prototype. planned recursively typecheck , assign properties new object , return object... but, there seems problem, see snippet of code:

object.prototype.copy = function() {     (prop in this)     {         console.log(prop); //logs copy (the function)!!!     } }  x = {"a": 1}; y = x.copy(); 

as i've pointed out in comment, found weird behavior, why happening? copy function should in object.prototype, not in instanced object itself! how fix it? can set this.copy = undefined, , still rely on object.prototype.copy?

this full code sample, requested:

object.prototype.copy = function() {     var object = this; //the object copying.     var newobject = {}; //the object return.      //cycle through properties of object creating, copy them recursively.     (prop in object)     {         if (!object.prototype.hasownproperty.call(this, prop) || object[prop] == null)         {             continue;         }          if (prop == "copy")         {             console.log("well, blah."); //this never prints!         }          if (typeof(object[prop]) == "object" && !(object[prop] instanceof array)) //if object's property object...         {             newobject[prop] = object[prop].copy(); //set copy of new object well.             console.log("1 --- " + prop); //this prints copy - 2 times! defies logic!         }         else if (typeof(object[prop]) == "object") //if it's array...         {             newobject[prop] = object[prop].slice(); //do in nicer fashion.             console.log("2 --- " + prop);         }         else //you're safe copy it.         {             newobject[prop] = object[prop];             console.log("3 --- " + prop + " --- " + object[prop]);         }     }      return newobject; } 

there's method called "hasownproperty" can use:

 if (this.hasownproperty(prop)) { ... } 

if function returns true it's "direct" property on object.

if fear "hasownproperty" method may borked, can this:

if (object.prototype.hasownproperty.call(this, prop)) { ... } 

instead.

newer versions of javascript have fancier ways of examining , controlling objects.

edit — updated code involves problem that'll bite due nested calls "copy": didn't declare "prop" var, after call copy object, value of "prop" have changed! (every call "copy" shares same variable, in other words.)