Filters out all elements that had the same filter applied on them before.
https://plugins.jquery.com/once/
JavaScript Libraries and Functions · jQuery Plugin
Get access to data on 1,143,061 websites that are jQuery Once Customers. We know of 158,353 live websites using jQuery Once and an additional 984,708 sites that used jQuery Once historically and 56,518 websites in the United States.
Get a list of 1,143,061 websites using jQuery Once which includes location information, hosting data, contact details, 158,353 currently live websites and an additional 280,740 domains that redirect to sites in this list. 984,708 sites that used this technology previouslyand 56,518 websites in the United States currently using jQuery Once.
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