How to check if a variable is loaded in JavaScript?

Question

How do I see if a certain object has been loaded, and if not, how can it be loaded, like the following?

if (!isObjectLoaded(someVar)) {
    someVar= loadObject()         


        

Answer 1

if(typeof(o) != 'object') o = loadObject();

Answer 2

if (!("someVar" in window)) {
  someVar = loadObject();
}

will tell you whether any JS has previously assigned to the global someVar or declared a top-level var someVar.

That will work even if the loaded value is undefined.

Answer 3

If you want to detect a custom object:

// craete a custom object
function MyObject(){

}

// check if it's the right kind of object
if(!(object instanceof MyObject)){
   object = new MyObject();
}

Answer 4

You can also just use a shortcut if(obj)