$$hashKey is an Angular variable that is attached to objects in ng-repeats. Its purpose is to track a list of objects. The value of $$hashKey is always the same for all requests. However, you might be wondering how it’s used.
$$hashkey attaches hash keys to objects, so that AngularJS knows when to update the DOM when a user changes a particular element. In addition, $$hashkey can be used to keep track of elements and items in an array so that Angular can apply changes to their counterparts.