Error in AngularJs: Unable to assign value to 'showGreeting' property because it is null

Currently, I am utilizing yeoman angularjs-fullstack for project generation. Now, my task is to customize it according to my preferences. I have limited experience with AngularJS and TypeScript, so any feedback would be greatly appreciated, not just the solution to why it isn't functioning. :)

Main.html:

    <div ng-if=main.isLoggedIn()>
    <div ng-if="main.timeOutGreeting()">
        <div ng-show="main.showGreeting">
            <header class="hero-unit" id="banner">
                <div class="container">
                    <h1>Hi!</h1>
                    <p class="lead">Welcome back, mr b>{{main.currentUser().name}}</b></p>
                </div>
            </header>
        </div>
    </div>
</div>

and mainController.ts:

'use strict';

(function() {

class MainController {

  showGreeting = true;

  constructor(Auth, $state, $timeout) {
    this.user = {};
    this.isLoggedIn = Auth.isLoggedIn;
    this.isAdmin = Auth.isAdmin;
    this.currentUser = Auth.getCurrentUser;

    this.$state = $state;
    this.$timeout = $timeout;

  }

  goToLogin() {
    this.$state.go('login');
  }

  timeOutGreeting() {
    this.$timeout(function() {
        this.showGreeting = false;
    }, 3000);
  }
}

angular.module('noteApp')
  .controller('MainController', MainController);

})();

The objective is to display "Hi! Welcome back, mr User" for a brief period (3 seconds) before disappearing. Any assistance in achieving this would be highly appreciated! :)

Answer №1

  1. Ensure you include the $scope "service" in your controllers constructor.

  2. Add a static $inject = ['service1', 'service2'] with all your services listed in the same order as in the constructor. Angular needs this to identify which services you require, especially when the script is minified.

  3. When using $timeout, make sure to utilize the lambda/fat arrow syntax for the function inside it. For example: this.$timeout(() => { this.$scope.main.showGreeting = true; });

The lambda syntax helps to maintain reference to the class' this object rather than the local functions' this object.

I trust these tips will be beneficial to you :)

Apologies for not providing an actual implementation sample, as I am currently using a phone.

Answer №2

Using an ng-if="..." statement with invalid JavaScript inside will not cause a browser error. Upon examining your code briefly, it appears that the variable "main" is never defined on $scope. To fix this issue, consider adding $scope.main = this; in your controller. This way, within your controller's scope, main will be a reference to the controller instance.

Answer №3

Utilize arrow functions for better performance!

delayedGreeting() {
    this.$timeout(() => {
        this.displayGreeting = false;
    }, 3000);
  }

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