Check if object exists in JavaScript

Question

How do I verify the existence of an object in JavaScript?

The following works:

if (!null)
   alert(\"GOT HERE\");

But this throws a

Answer 1

Apart from checking the existence of the object/variable you may want to provide a "worst case" output or at least trap it into an alert so it doesn't go unnoticed.

Example of function that checks, provides alternative, and catch errors.

function fillForm(obj) {
  try {
    var output;
    output = (typeof obj !== 'undefined') ? obj : '';
    return (output);
  } 
  catch (err) {
    // If an error was thrown, sent it as an alert
    // to help with debugging any problems
    alert(err.toString());
    // If the obj doesn't exist or it's empty 
    // I want to fill the form with ""
    return ('');
  } // catch End
} // fillForm End

I created this also because the object I was passing to it could be x , x.m , x.m[z] and typeof x.m[z] would fail with an error if x.m did not exist.

I hope it helps. (BTW, I am novice with JS)