Error message: Updating Ionic has caused an issue where the data type 'string' cannot be assigned to the data type 'null'. This error is labelled as ts(2322)

For over two years, I've been using the code below for a side menu in Ionic up to version 5. However, after updating to Ionic 6.20.6 and Angular 15^, I encountered the following error:

else { this.showLevel1 = idx; }

Type 'string' is not assignable to type 'null'.ts(2322)

export class AppComponent {
  public appPages: any;
  showLevel1 = null;
  showLevel2 = null;
   @ViewChildren(IonRouterOutlet) routerOutlets: QueryList<IonRouterOutlet>;

  
 
  clearLevel() {
    this.showLevel1 = null;
    this.showLevel2 = null;
  //  this.showLevel3 = null;
  }
  toggleLevel1(idx: string) {
    if (this.isLevel1Shown(idx)) {
      this.showLevel1 = null;
    } else {
      this.showLevel1 = idx;
    }
    
  }
  isLevel1Shown(idx: string) {
    
    return this.showLevel1 === idx;
  }
angulartypescriptionic-frameworktypeerror

Answer №1

The most recent version of Ionic now includes string typing functionality. Make sure to assign an empty string if you plan on using a variable or member variable as a string. For example:

level1: string = "";

Answer №2

Following the advice provided by - [Andru Alen]1 in the comments of my post, I implemented the suggested changes and they worked perfectly for me. Here is the updated code snippet:

   public appPages: any;
  showLevel1: string | null = null;
  showLevel2: string | null = null;
   @ViewChildren(IonRouterOutlet)
  routerOutlets!: QueryList<IonRouterOutlet>;

  
  constructor(
    private platform: Platform,

    private router: Router,
    private data: DataService
  ) {
    
   // this.backButtonEvent();
    this.data.getData().subscribe((resp) => {
   //   console.log(resp);
      this.appPages = resp;
    });
   
  }

  clearLevel() {
    this.showLevel1 = null;
    this.showLevel2 = null;
  //  this.showLevel3 = null;
  }
  toggleLevel1(idx: string) {
    if (this.isLevel1Shown(idx)) {
      this.showLevel1 = null;
    } else {
      this.showLevel1 = idx;
    }
    
  }`enter code here`
  isLevel1Shown(idx: string) {
    
    return this.showLevel1 === idx;`d`
  }`enter code here`

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