Why is null considered an object in JavaScript?  Is checking   if ( object == null )       Do something   the same as   if ( !object )       Do something   ?  And also:  What is the difference between null and undefined?...

In my particular case:  callback instanceof Function   or   typeof callback == "function"   does it even matter, what's the difference?  Additional Resource:  JavaScript-Garden typeof vs instanceof...

Is there a better way to get the type of a variable in JS than typeof? It works fine when you do:  > typeof 1 "number" > typeof "hello" "string"   But it's useless when you try:  > typeof [1,2] "object"...

I have a window, where before being closed I refresh the underlying page.  if(opener && typeof(opener.Refresh) != 'undefined') {     opener.Refresh(); }   If I moved away from the original opening page, this code would throw a "Pe...

One can use typeof to determine whether a value is primitive or boxed.   Consider:  typeof "foo"; // "string" typeof new String("foo"); // "object"   In combination with Object.prototype.toString we could define the fo...

I'm trying to use some of the more advanced OO features of Javascript, following Doug Crawford's "super constructor" pattern. However, I don't know how to set and get types from my objects using Javascript's native type system...

In this question I did not see suggestions to use constructor.  So instead of typeof callback == "function"  I would use callback && (callback.constructor==Function).  To me it seems obvious that comparison to memory pointers is alway...

I have a flash object (HTMLObjectElement) created (with jQuery) and added it to the DOM. That is working OK in all browsers. This object is saved/stored in a variable called "o.data.cam". Other functions checking this variable if it is valid....

I thought this would be as easy as:  if(typeof(Array.push) == 'undefined'){   //not defined, prototype a version of the push method   // Firefox never gets here, but IE/Safari/Chrome/etc. do, even though   // the Array object has a push metho...

In Chrome and Firefox,  typeof foo   evalulates to 'undefined'.  But  typeof (function() { return foo; })()   throws an error:  ReferenceError: foo is not defined   This destroys the notions that I have of susbstitutability of expressions! Un...