Handling promises in Angularjs

Question

I would like to know how to handle promises properly when there is a condition involved too.

For example I have this code:

if(something == true) {
  loginObj.$login("anonymous").then(function(){ //handling the promise
    //do something with the promise
    //do something line 1
    //do something line 2
    //do something line 3
    //do something line 4
    //do something line 5
  });
}
else {
  //do the same thing line 1
  //do the same thing line 2
  //do the same thing line 3
  //do the same thing line 4
  //do the same thing line 5
}

I hope you can see my problem. If something is true then I will have to wait for the promise to resolve before executing my lines of code. However, my else block contains nearly all the same lines of code but I'm having to repeat myself.

Why can I do to avoid this duplication?

execute the repeated lines in a 'finally'

mccainz
– mccainz

2014-09-23 16:29:57 +00:00
Commented Sep 23, 2014 at 16:29 — mccainz
– mccainz, Commented Sep 23, 2014 at 16:29
could you give me an example?

tommyd456
– tommyd456

2014-09-23 16:30:28 +00:00
Commented Sep 23, 2014 at 16:30 — tommyd456
– tommyd456, Commented Sep 23, 2014 at 16:30

graphefruit · Accepted Answer · 2014-09-23 16:29:29Z

1

Lay down a function to call?

$scope.doTheSame= function()
{

}

if(something == true) {
  loginObj.$login("anonymous").then(function(){ //handling the promise
    //do something with the promise
    $scope.doTheSame()
  });
}
else {
  $scope.doTheSame()
}

And pass needed parameters, or if you're working with scope objects you can still acess them

answered Sep 23, 2014 at 16:29

graphefruit

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2 Comments

tommyd456 Over a year ago

Sorry I think you're missing my point. I know about functions

graphefruit Over a year ago

So maybe clearify the problem, you don't wanna write code twice, what stands against to use a function for this?

Fordio · Accepted Answer · 2014-09-23 16:33:47Z

1

if(something == true) {
  loginObj.$login("anonymous").then(function(){ //handling the promise
    //do something with the promise
    doSomething();
  }).
  catch(function() { // catch code } ).
  finally(function() { // finally code });
}
else {
  doSomething()
}

function doSomething() {
  //do the same thing line 1
  //do the same thing line 2
  //do the same thing line 3
  //do the same thing line 4
  //do the same thing line 5
}

answered Sep 23, 2014 at 16:33

Fordio

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Comments

mccainz · Accepted Answer · 2014-09-23 17:11:48Z

Execute the repeated lines in a 'finally/always' block.

For instance if using $q,

var outputPromise = getInputPromise()
.fin(function () {
    // close files, database connections, stop servers, conclude tests
});

Or if using Jquery...

$.get( "test.php" ).always(function() {
  alert( "$.get completed with success or error callback arguments" );
});

Alternately if your code cannot be structured such that the login alternate methods can flow in a promise chain then you can simply remove both login functions to a single function which returns a promise and then chain that function, as below.

http://plnkr.co/edit/nJRaBb04JpLdHicgxg2u?p=preview

<!DOCTYPE html>
<html>

  <head>
    <script data-require="jquery@*" data-semver="2.1.1" src="//cdnjs.cloudflare.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
    <link rel="stylesheet" href="style.css" />
    <script src="script.js"></script>
  </head>

  <body>
    <h1>Hello Plunker!</h1>
    <button id="loginBtn">Login</button>

    <script>

    function login1(){
       var $def =$.Deferred();
       window.setTimeout(function(){
         $def.resolve("loginMethod1");
       },1000);
       return $def.promise();
    }

    function login2(){
       var $def =$.Deferred();
       window.setTimeout(function(){
         $def.resolve("loginMethod2");
       },1000);
       return $def.promise();
    }

    function login(val){
      var $def =$.Deferred();
      if(val){
        login1().then(function(res){
           $def.resolve(res);
        });
      }
      else{
        login2().then(function(res){
           $def.resolve(res);
        });
      }
      return $def.promise();
    }

    $("#loginBtn").bind("click",function(){
        login(Math.random()>0.5)
        .then(function(res){
          console.log(res + " ...do everythign else here");
        });
    });

    </script>
  </body>

</html>

marneborn · Accepted Answer · 2014-09-23 17:40:04Z

I like using $q.when()/$q.reject() to create a resolved promise in situations like this.

var promise;
if ( something === true ) {
    promise = loginObj.$login("anonymous")
    .then(
        function(){ //handling the promise
            //do something with the promise
        }
     );
}
else {
    promise = $q.when("somethingelse");
    //promise = $q.reject("somereason");
}
promise.then(
    function (somethingelse) {
        //do something line 1
        //do something line 2
        //do something line 3
        //do something line 4
        //do something line 5
    }
);

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