Could someone explain this to me? Underscore JS library

I saw this code but don't understand it?
 if (!window.__) {
            window.__ = window._;
        }

Open in new window

What is the purpose? it is in reference to the javascript underscore library being loaded dynamically or using a static version on the page.

Thanks!
894359Asked:
Who is Participating?

[Product update] Infrastructure Analysis Tool is now available with Business Accounts.Learn More

x
I wear a lot of hats...

"The solutions and answers provided on Experts Exchange have been extremely helpful to me over the last few years. I wear a lot of hats - Developer, Database Administrator, Help Desk, etc., so I know a lot of things but not a lot about one thing. Experts Exchange gives me answers from people who do know a lot about one thing, in a easy to use platform." -Todd S.

Julian HansenCommented:
In JavaScript $ and _ are treated as characters - so they are legal in terms of defining function names.

In other words

function _(a)
{
   alert(a);
}
_('Boo');

Open in new window

Is valid and will popup an alert with Boo in it
Consider the following code
// SET GLOBAL FUNCTION _ TO alert('boo')
window._ = function() {alert('boo');}

// CHECK IF GLOBAL FUNCTION __ EXISTS AND IF IT DOES NOT
// SET IT EQUAL TO function _
if (!window.__) {
	window.__ = window._;
}
// THIS WILL SHOW ALERT WITH 'boo'
window.__();

Open in new window

Experts Exchange Solution brought to you by

Your issues matter to us.

Facing a tech roadblock? Get the help and guidance you need from experienced professionals who care. Ask your question anytime, anywhere, with no hassle.

Start your 7-day free trial
It's more than this solution.Get answers and train to solve all your tech problems - anytime, anywhere.Try it for free Edge Out The Competitionfor your dream job with proven skills and certifications.Get started today Stand Outas the employee with proven skills.Start learning today for free Move Your Career Forwardwith certification training in the latest technologies.Start your trial today
JavaScript

From novice to tech pro — start learning today.