类型“any [] | undefined”不能分配给类型“any []”

Question

i have a new problem since i updated today my npm and all modules. Everything worked before i did the update.

error is "the type "any [] | undefined" cannot be assigned to the type "any []""

code

    this.myservice.myfunction().toPromise().then((data)=>{
      this.variable = data;
    }).catch((error)=>{
      console.log("Promise rejected with " + JSON.stringify(error));
    });

and in the service:

  myfunction(): Observable<any[]> {
    return this.http.post<any[]>(`${this.baseUrl}/GetDataFromBackend`, {  }).pipe(
      map((res) => res),
      catchError(this.handleError));
  }

anyone an idea why i got this error after the update? How can i fix this? i got this at nearly every component and backend connection...

Answer 1

This is a typescript error. You can overcome the problem in several ways.

1: You can check for undefined like this:

    this.myservice.myfunction().toPromise().then((data)=>{
       if(data !== undefined && data !== null) {
          this.variable = data;
      }
    }).catch((error)=>{
      console.log("Promise rejected with " + JSON.stringify(error));
    });

2-if you know the value will never be undefined you can force it with ":" like this:

    this.myservice.myfunction().toPromise().then((data)=>{
       
          this.variable = data!;
      
    }).catch((error)=>{
      console.log("Promise rejected with " + JSON.stringify(error));
    });

3- you can change the type of the variable when you declare it to be like:

let variable: any [] | undefined = [];

I am sure there is a couple more ways to fix this issue. But these 3 are the most commonly used in my personal experience.

With the advantage that you dont have to disable nice features like "strict" globally in your project.

The point is to develop using a stricter strongly typed model and not to weaken your code by "lowering the bar" on the typescript.