AngularJS input not updating with ng-model - angularjs

Question

I have a form with three input fields:
<form name="myForm" novalidate ng-controller="MainController as vm">
<div>
<input type="text" ng-model="vm.id" name="idInput" required>
<input type="email" ng-model="vm.email" name="emailInput" required>
<input type="text" ng-model="vm.output" name="output">
</div>
</form>
vm.output is a variable defined in my controller that contains some strings plus vm.id and vm.email:
vm.output = 'myurl.com?id=' + vm.id + '&email=' + vm.email;
I want to generate an output URL based on the user input in the id and email fields. However, the output-field does not update when I enter some input into the two other fields. It just says myurl.com?id=undefined&email=undefined,
I can get it working if I use
ng-value="'myurl.com?id=' + vm.id + '&email=' + vm.email"
However, I'm using ng-clip which gets the content to copy by using ng-model so I need to use that.
Also, here's my controller:
angular
.module("app")
.controller("MainController",[MainController);
function MainController(){
var vm = this;
vm.output = 'myurl.com?id=' + vm.id + '&email=' + vm.email;
}
Any suggestions?

Answer 1

You could accomplish this a few different ways. One way is to set up ng-change events on each of the inputs you want to watch:
<div>
<input type="text" ng-model="vm.id" ng-change="updateOutput()" name="idInput" required />
<input type="email" ng-model="vm.email" ng-change="updateOutput()" name="emailInput" required />
<input type="text" ng-model="vm.output" name="output" />
</div>
Then, you have to build the update method on the controller scope:
app.controller = app.controller('MainController', function($scope) {
$scope.vm = {
output: '',
email: '',
id: ''
};
$scope.updateOutput = function() {
$scope.vm.output = 'myurl.com?id=' + $scope.vm.id + '&email=' + $scope.vm.email;
}
});
Here is a working plunker.

Answer 2

I would go with custom directive that would set model value properly:
app.directive('concatModel', function($parse) {
var pattern = function(data) {
return 'myurl.com?id=' + data.id + '&email=' + data.email;
};
return {
require: 'ngModel',
scope: {
data: '=concatModel'
},
link: function(scope, element, attrs, controller) {
scope.$watchCollection('data', function(newVal) {
controller.$setViewValue(pattern(newVal));
controller.$render();
});
}
};
});
and use it like this:
<div>
<input type="text" ng-model="vm.id" name="idInput" required="" />
<input type="email" ng-model="vm.email" name="emailInput" required="" />
<input type="text" concat-model="{id: vm.id, email: vm.email}" ng-model="vm.output" name="output" />
</div>
Demo: http://plnkr.co/edit/sFW16LLZK3TezNAvYk5F?p=info