jQuery: Understanding .done() and .fail()

Question

I'm jumping into a project authored by another developer, and am trying to make my way around the codebase.

Here's the code I'm having trouble with:

var ret;
ret = new $.Deferred();

new Parse.Query(Model).include('companyDetails').matchesQuery('companyDetails', 
new Parse.Query(UserModel).equalTo('objectId', 'seppWfGi20')).first().done((function(_this) {
  return function(person) {
    if (person) {
      _this.data.person = person;
      return ret.resolve(_this.data.person);
    } else {
      return ret.reject('person');
    }
  };
})(this)).fail((function(_this) {
  return function(error) {
    return ret.reject('person');
  };
})(this));

ret;

I can't work out what the .done() and .fail() methods are doing. Also, what's the .first() there for?

Can any jQuery ninjas help explain what this code is doing, step-by-step?

Any help is appreciated. Thanks in advance!

Answer 1

These are a form of promises . In this instance, it allows explicit functions to be called when success/failure happens. It's the equivalent of doing…

Parse.query({query here}, {
    success: function(response){}, // this is the done function
    error: function(response){} // this is the fail function
})

Finally, the .first() is Parse specific telling it to get the first result in the query set. I'd say you'd be better off untangling that mess of IIFE statements.