jQuery / Javascript code check, if not undefined

I like this:

if (wlocation !== undefined)

But if you prefer the second way wouldn't be as you posted. It would be:

if (typeof wlocation  !== "undefined")

I generally like the shorthand version:

if (!!wlocation) { window.location = wlocation; }

$.fn.attr(attributeName) returns the attribute value as string, or undefined when the attribute is not present.

Since "", and undefined are both falsy (evaluates to false when coerced to boolean) values in JavaScript, in this case I would write the check as below:

if (wlocation) { ... }