what is the difference between deferred.resolve(data); and deferred.resolve(); in angularJS service calls?

Question

I found 2 variation like 1. deferred.resolve(); 2. deferred.resolve(data);

after service response. What is the difference between 2. Which one I have to use strictly.

Answer 1

First scenario:

function getPromise() {
    var deferred = $q.defer();
    deferred.resolve();

    return deferred.promise;
}

getPromise().then(
    function(data) {
        console.log(data); // Output "undefined"
    }
);

Second scenario:

function getPromise() {
    var deferred = $q.defer();
    var data = "hello";
    deferred.resolve(data);

    return deferred.promise;
}

getPromise().then(
    function(data) {
        console.log(data); // Output "'hello'"
    }
);

So it all about on how you resolve the promise, with or without passing information to the function in the resolved promise.

Answer 2

When you call a service, it mean that you're waiting for a server's response. The response could be a simple success or some data.

myServiceFunction = function() {
    var deferred = $q.defer();
       $http.post/get(myURL,someData/*not mandatory*/)
          .success(function(response){ // you get into this function when everything goes right
               deferred.resolve(response); //your sending back the server's response to your controller (or whatever has called this function)
        })
         .error(function(response){
              deferred.reject(response); // your also sending back the server's response but using reject means that something gone wrong on server call
    })
    return deferred.promise; // don't forget to send the promise!!
}

In the example above I'm sending the response server back to the one which has called the service function.

But if you just need to know that the request succeeded then a simple deferred.resolve() is enough (and deferred.reject() - to tell that it didn't succeed).

To make it shorter, here's what you should know:

• deferred.resolve() - means request succeeded
• deferred.reject() - request failed
• deferred.resolve(data) - means request succeeded and here's some data
• deferred.reject(data) - request failed and here;s some data

Hope it's clear enough