firebase - Need help understanding this promise and handling the error -

i saving data firebase database inside polymer element. works fine. person who's new promises need understand promise.resolved() means here @ end of method. isn't promise going through before when .then used? doing? looked around can't find example of resolved() no value.

and how can change have more familiar structure below:

.then(function(snapshot) {   // promise "fulfilled" (it succeeded). }, function(error) {   // promise rejected. }); 

here's block , promise.resolved() taken documentation:

savedata : function() {                     this.$.document.data = this.$.message.value;            this.$.document.save("/parent", "child").then(function() {             console.log('sent event!!!!!!');             this.$.document.reset();           }.bind(this));           return promise.resolve();         }, 

first need understand basics of promises.

lets start basics -

a newly created es6 promise in 1 of following states:

• resolved
• rejected
• pending --> waiting either resolved or rejected

lets create sample promise

var promise = new promise(function(fulfill, reject) {   // stuff , either fullfill or reject promise }); 

so above promise receives callback function called executor function signature function(fullfill, reject).

a newly created promise has important property function called then used chaining , controlling logic flows.

then takes 2 optional callback parameters onfulfilled , onrejected.

inside executor function 2 things happens indicate outcome of promise -

• fullfill method gets called or without value:

  means operation completed successfully. if call fulfill value onfulfilled callback in then receive value, if decided not provide value in fulfill call onfulfilled called parameter undefined.

  var promise = new promise(function(fulfill, reject) {    // lets assume operation completed    fulfill('success'); });  promise.then(onfulfilled, onrejected);  function onfulfilled(result) {      console.log(result);      // success printed } 

• reject method gets called or without value:
  problem occurred while performing operation. can decided whether pass error message reject callback indicate error occurred end user.

  var promise = new promise(function(fulfill, reject) {    // lets assume operation did not complete    reject(new error('error')); });  promise.then(onfulfilled, onrejected);  function onrejected(error) {      console.log(error.message);      // error message printed } 

now lets talk promise.resolve.

at top learned how create promise through constructor.

var promise = new promise(function (fulfill, reject) {   fulfill('success value'); });  // now: promise.resolve // same thing above code  var promise = promise.resolve('success value'); 

similarly comes promise.reject -

var promise = new promise(function (fulfill, reject) {   reject(new error('error value')); });  var promise = promise.reject(new error('error value')); 

in case save seems returning promise , internally promise may calling either fulfill or reject method don't need call promise.resolve(). need values returned promise either fulfilled value or rejected value in then method.

 savedata : function() {                 this.$.document.data = this.$.message.value;        // return promise       return this.$.document.save("/parent", "child");  }  savedata() .then(function() {         console.log('sent event!!!!!!');         this.$.document.reset();       }.bind(this)); 

i hope makes things promises clearer.