How this function is passing value to the second function? [closed]

Please describe this function that is passing authenticated user to the handler? how it passing and how the handler is getting it? This is the global function:

window.Vue.prototype.authorize = function(Handler){
    return Handler(window.App.user);
};

This is the where it is called:

this.authorize(user => this.attributes.user_id!==user.id);