Multiple then() calls fire in order

Because each then() returns a new promise, original order is preserved.

by jdmarshall

HTML

<script src="https://code.angularjs.org/1.2.12/angular.js"></script>
<div ng-controller="MyCtrl">
    <h2>Promise.then() calls resolve in order</h2>
    <div class="output">Output: {{output}}</div>
    <div class="input">
        <button ng-click='doClick()'>Click me</button>
    </div>
</div>

CSS

body{
    padding: 10px;
}

.input, .output {
    padding: 10px;
}

.output {
    height: 20px;
}

JavaScript

var myApp = angular.module('myApp',[]);

function MyCtrl($scope, $q) {
    $scope.output = "";
    
    var deferred = $q.defer();
    deferred.promise.then(function(val) {
        $scope.output = val;
    }).then(function(val) {
        $scope.output += "B";
    }).then(function(val) {
        $scope.output += "C";
    }).then(function(val) {
        $scope.output += "D";
    });
    
    $scope.doClick = function() {
        deferred.resolve("A");
    };
}