Nicer way of checking JavaScript namespace

Question

Now I have a module which follows a long chain of namespaces, for example:

TOP.middle.realModuleName = function () { /*...*/ }

I need to use this module on a page, and I'm not sure if this page has included the namespace Top.middle. So I would have to do something like:

if (typeof TOP !== 'undefined' && TOP.middle && TOP.middle.realdModuleName) {
    new TOP.middle.realModuleName();
}

I think the if statement looks really long and verbose. Anyone has suggestions on how to write a nicer parameter checking pattern for this case?

Answer 1

Try this simple helper function:

function exists(namespace) {    
   var tokens = namespace.split('.');
   return tokens.reduce(function(prev, curr) {
      return (typeof prev == "undefined") ? prev : prev[curr];
   }, window);
}

It takes a String as input and will return the object if it exists. You can use it like this:

var module = exists("TOP.middle.realModuleName");

For example:

exists("noexist"); // returns undefined
exists("window"); // returns DOMWindow
exists("window.innerHeight"); // returns Number
exists("window.innerHeight.toString"); // returns Function
exists("window.innerHeight.noexist"); // returns undefined

It also works properly for expressions that evaluate to false:

testNum = 0;
testBool = false;
testNull = null;

exists("testNum"); // returns 0
exists("testBool"); // returns false
exists("testNull"); // returns null

Answer 2

just encapsulate it in a TRY/CATCH?

try {
    return new TOP.middle.blablabla();
}
catch(err) {
    // oh no!
}

return null;