Do Typescript code require the use of a constructor?

After initializing a fresh Aurelia project using the aurelia-cli and executing the au new command, I received the following app.ts:

export class App {
  message = 'Hello World!';
}

To enhance my app.ts, I replaced it with the code from a helpful tutorial. The updated code now looks like this:

export class App {
  constructor() {
    this.message = 'Hello World!';
    this.firstName = "Animesh";
    this.lastName = "Bulusu";
  }

  get fullName() {
    return `${this.firstName} ${this.lastName}`;
  }
}

When refreshing the page, everything displays correctly. However, I notice some errors in the console:

Property 'message' does not exist on type 'App'.
Property 'lastName' does not exist on type 'App'.
Property 'lastName' does not exist on type 'App'.

The errors disappear if I eliminate the constructor and directly declare the variables within the class. What is causing this behavior, and how can I eliminate these errors?

Answer №1

To resolve the issue, ensure that you declare the members as shown below:

class App {
    private message: string;
    private firstName: string;
    private lastName: string;

    constructor() {
        this.message = 'Hello World!';
        this.firstName = "Animesh";
        this.lastName = "Bulusu";
    }
 }

By doing so, the errors should disappear.


Edit

If your initial member values are constants and you don't need to initialize anything when creating a new instance, consider omitting the constructor like this:

class App {
    private message = 'Hello World!';
    private firstName = "Animesh";
    private lastName = "Bulusu";
}

(Note that specifying the type of the members is unnecessary here as the compiler can infer that they are strings)

Alternatively, if you want the members to be assigned values passed to the constructor, you can use the shortcut (similar to what is seen in C#):

class App {
    constructor(private message: string, public name: string) {}
}

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