How to use in jQuery :not and hasClass() to get a specific element without a class

Use the not function instead:

var lastOpenSite = $(this).siblings().not('.closedTab');

hasClass only tests whether an element has a class, not will remove elements from the selected set matching the provided selector.

It's much easier to do like this:

if(!$('#foo').hasClass('bar')) { 
  ...
}

The ! in front of the criteria means false, works in most programming languages.

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