In IE 6/7/8 you can't delete elements from the window object. It is possible to delete "global" variables (there is a slight distinction there) but only if they were not declared as properties of window.

http://jsfiddle.net/CX3dk/

http://perfectionkills.com/understanding-delete/

I am not sure of the history of why the property is defined on window, or whether it is wise to change that.

Is this affecting you in some way, or simply a sanitation thing?

It tripped me up when using jQuery and Zepto.

I realise this is a slightly odd situation but I'm using the same code on mobile and desktop and due to doing slightly different things my code has ended up as:

<browser only>

Include jQuery

My code using jQuery

jQuery.noConflict();

</browser only>

<common code (runs on browser and mobile>

Include Zepto

My code relying on Zepto

</common code>

Zepto only sets $ if ('$' in window) is false, so my code ran fine on mobile but $ was undefined on desktop.

This seems like something Zepto should handle, since we've worked this way since day one. I guess they don't have to worry about IE6/7/8 issues but we do.

Its a bit hard for Zepto to know what to do, if Zepto sees $ is set to undefiend how does it know whether I'm using $ for something else and undefined is a meaningful value for me, or its been "unset" by jQuery or similar.

Sure, if there is a solution that preserves IE 6/7/8 compatibility we could include it. If not, you can just delete window.$ after your jQuery.noConflict() call.

#14013 is a duplicate of this ticket.