.has()

Reduce the set of matched elements to those that have a descendant that matches the selector or DOM element.

.promise()

Return a Promise object to observe when all actions of a certain type bound to the collection, queued or not, have finished.

jQuery.each()

A generic iterator function, which can be used to seamlessly iterate over both objects and arrays. Arrays and array-like objects with a length property (such as a function’s arguments object) are iterated by numeric index, from 0 to length-1. Other objects are iterated via their named properties.