Error message: "An issue has been encountered within Angular 4 where it is

Question

Error message: "An issue has been encountered within Angular 4 where it is

Thank you for any assistance, I realize this may be a beginner question... but I seem to be missing something and my TypeScript code is error-free.

My goal is simple: I want to track which Main Menu Item is currently selected.

To achieve this, I have bound my HTML using variables in the following way: (if there's a direct way to bind an enum value, please let me know).

<div id ="menu_popular" class="{{menuClass}}" style="left:90px; top:368px;">
  Menu Item
</div>

Next, I thought of updating my code declarations by calling a function selectMenu like so:

import {Component} from '@angular/core';
import {MainMenuItem} from './domain';

@Component ({
          selector: 'app-root',
          templateUrl: './app.component.html',
          styleUrls: ['./app.component.css']
        })
export class AppComponent
{
  title = 'Angular App';
  menuClass = 'div.menu_text';

}

let selectedItem: any = MainMenuItem.POPULAR;

const selectMenu = function (item: MainMenuItem) {
  console.log ('Switching Selected Menu from: ' + selectedItem + ' to: ' + item);
  selectedItem = item;
  console.log('Assigned');
  console.log(this.AppComponent.menuClass);
  if (item === MainMenuItem.YEIIIII)
  {
 ...
 selectMenu (MainMenuItem.YEIIIII);

However, when I tried that, I encountered a runtime error stating Cannot read property 'AppComponent' of undefined.

It seems I'm unable to access the values of AppComponent in any way,

console.log(this.AppComponent.menuClass);

or

console.log(this.menuClass);

What am I missing here?

Thanks!

angular typescript

Answer 1

Answer №1

If you have multiple menu items that need to be selected, one simple solution is to store all the menu items in an array within your `.ts` file.

menuItem:string[] = ['item1', 'item2', 'etc'];
selectedItem: number = 0;
menuClass = 'div.menu_text';

In your `html` file, you can display these menu items like this:

<div
    *ngFor="let item of menuItem; let i=index"
    (click)="selectedItem = i"
    [ngClass]="selectedItem==i ? menuClass:''">{{item}}
</div>

This HTML code loops through the `menuItem` array and displays the items on the page. In this case, it would create 3 divs based on the array. The `let item of menuItem` line not only iterates through the array but also declares an index variable for each iteration. Each menu item displayed has a click event attached to it. When clicked, the `selectedItem` is set to the index value of that particular item. The `[ngClass]` directive allows us to conditionally add a class - in this case, `selectedItem==i ? menuClass:''`. If the `selectedItem` matches the index of the current menu item, the `menuClass` styling is applied; otherwise, no additional class is added.

This approach may not be the best solution for every scenario, but hopefully, it gives you some insight into how you could tackle this issue.

Answer 2

If you have multiple menu items that need to be selected, one simple solution is to store all the menu items in an array within your `.ts` file.

menuItem:string[] = ['item1', 'item2', 'etc'];
selectedItem: number = 0;
menuClass = 'div.menu_text';

In your `html` file, you can display these menu items like this:

<div
    *ngFor="let item of menuItem; let i=index"
    (click)="selectedItem = i"
    [ngClass]="selectedItem==i ? menuClass:''">{{item}}
</div>

This HTML code loops through the `menuItem` array and displays the items on the page. In this case, it would create 3 divs based on the array. The `let item of menuItem` line not only iterates through the array but also declares an index variable for each iteration. Each menu item displayed has a click event attached to it. When clicked, the `selectedItem` is set to the index value of that particular item. The `[ngClass]` directive allows us to conditionally add a class - in this case, `selectedItem==i ? menuClass:''`. If the `selectedItem` matches the index of the current menu item, the `menuClass` styling is applied; otherwise, no additional class is added.

This approach may not be the best solution for every scenario, but hopefully, it gives you some insight into how you could tackle this issue.

Answer 3

Answer №2

Make sure not to assign the this keyword if you wish to access the component itself. Your function's scope is limited by your const variable, however, using an arrow function would give you access to the window scope (similar to global).

sample code

export class AppComponent implements AfterContentInit{

  constructor(
    private elementRef:ElementRef
  ) { }

  title = 'Angular App';
  menuClass = 'div.menu_text';
  public selectedItem: any = MainMenuItem.POPULAR;

  ngAfterContentInit(){
    this.selectMenu (MainMenuItem.YEIIIII);
  }

  selectMenu(item: MainMenuItem) {
    console.log('Switching Selected Menu from: ' + this.selectedItem + ' to: ' + item);
    this.selectedItem = item;
    console.log('Assigned');
    console.log(this.menuClass);
    if (item === MainMenuItem.YEIIIII) { }
  }

}

Answer 4

Make sure not to assign the this keyword if you wish to access the component itself. Your function's scope is limited by your const variable, however, using an arrow function would give you access to the window scope (similar to global).

sample code

export class AppComponent implements AfterContentInit{

  constructor(
    private elementRef:ElementRef
  ) { }

  title = 'Angular App';
  menuClass = 'div.menu_text';
  public selectedItem: any = MainMenuItem.POPULAR;

  ngAfterContentInit(){
    this.selectMenu (MainMenuItem.YEIIIII);
  }

  selectMenu(item: MainMenuItem) {
    console.log('Switching Selected Menu from: ' + this.selectedItem + ' to: ' + item);
    this.selectedItem = item;
    console.log('Assigned');
    console.log(this.menuClass);
    if (item === MainMenuItem.YEIIIII) { }
  }

}

Error message: "An issue has been encountered within Angular 4 where it is

Answer №1

Answer №2

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