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JavaScript AngularJS Extending Inputs Extending Inputs: Optional require

check is controller defined

can somebody help me with this task please? I dont get it :/

angular.module('treehouseCourse', [])
  .directive('sometimesTwoWay', function() {
    return {
      require: '?ngModel',
      link: function($scope,$element,$attrs,ngModelCtrl){}
<!DOCTYPE html>
<html ng-app="treehouseCourse">
  <script src="js/angular.js"></script>
  <script src="app.js"></script>

  <sometimes-two-way ng-model="course.description"></sometimes-two-way>


2 Answers

The controller should be the value passed to the parameter ngModelCtrl in the link function. It will either be defined (passed a value) or by default, will be undefined, as any parameter not passed into a function would be in JavaScript.

So you're essentially testing if ngModelCtrl equals undefined.

The simplest way to do that is a conditional with a logical NOT operator:

if (!ngModelCtrl) {
  // ngModelCtrl is undefined

OR of course, you can leave out the ! and check first to see if it is defined:

if (ngModelCtrl) {
  // ngModelCtrl is defined
} else {
  // ngModelCtrl is undefined

Hope that helps!

Thank you Iain :)

No problem. You should probably mark the answer as 'Best Answer' if it answered your question, that way other students know your question has been answered/closed.