Opposed to my expectation I can't access my class field myLibrary in the class method initialize().

class ViewController {
      myLibrary = new Library();
      initialize() {
        console.log(myLibrary); // undefined

The only "solution" I found was to declare myLibrary outside of the class as a global variable. Is there a way to declare fields in a class and then, well, use them?

CodePudding user response：

JavaScript classes do not work the same way as Java classes.

To access properties on an object you need to state the object and then access a property on it. They aren't treated as variables in the current scope.

Inside a method, the keyword this will give you the associated object. (See How does the "this" keyword work? for a less simplified explanation).

So you need this.myLibrary instead of just myLibrary.

CodePudding user response：

class Library {
  …
}

class ViewController {
  constructor() {
    this.myLibrary = new Library();
  }

  log() {
    console.log(this.myLibrary);
  }
}

const viewController = new ViewController();
viewController.log()

CodePudding user response：

Use this to access properties of your object.

class ViewController {
      constructor(){
          this.myLibrary = new Library();
      }

      initialize() {
        console.log(this.myLibrary); // 
}

An example from mdn:

class Person {
    constructor(firstName, lastName) {
        this.firstName = firstName;
        this.lastName = lastName;
    }

    // Getter
    get firstNameAndLastName() {
       return this.calcFullName();
    }

    // Method
    calcFullName() {
        return `${this.firstName} ${this.lastName}`;
    }
}