JavaScript if var exists

Question

I want my code so that if a specific var exists it will perform an action, else it will be ignored and move along. The problem with my code is, if the specific var does not exist it causes an error, presumably ignoring the remainder of the JavaScript code.

Example

var YouTube=EpicKris;

if ((typeof YouTube) != 'undefined' && YouTube != null) {
    document.write('YouTube:' + YouTube);
};

Answer 1

try {
  if(YouTube) {
    console.log("exist!");
  }
} catch(e) {}
console.log("move one");

Would work when YouTube is not null, undefined, 0 or "".

Does that work for you?

Answer 2

This is a classic one.

Use the "window" qualifier for cross browser checks on undefined variables and won't break.

if (window.YouTube) { // won't puke
    // do your code
}

OR for the hard core sticklers from the peanut gallery...

if (this.YouTube) {
    // you have to assume you are in the global context though 
}

Answer 3

Code:

var YouTube=EpicKris;

if (typeof YouTube!='undefined') {
    document.write('YouTube:' + YouTube);
};

Worked out the best method for this, use typeof to check if the var exists. This worked perfectly for me.