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Implicit return in a javascript class method

Suppose I have this code:

class AuthService {
  loginWithEmailAndPassword(email, password) {
    return apolloClient.mutate({});
  }
}

export default new AuthService();

is there a modern way to write loginWithEmailAndPassword to have an implicit return?

about 4 years ago · Juan Pablo Isaza

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Accepted Answer · 2022-08-31T07:27:21.315Z

Yes, using the newer public class fields feature, you can add the function to your instance.

class AuthService {
  loginWithEmailAndPassword = (email, password) => (
    { email, password }
  )
}

const authService = new AuthService()
console.log(authService.loginWithEmailAndPassword('x@y', 'Password!'))

Note that there's a couple differences when you do this:

Arrow functions automatically bind the "this" value whereas normal functions do not (in general, this is a good thing anyways)
This function will be added onto the instance, not the prototype. This has important consequences if you expect others to be inheriting your class.

An example of the second point:

class BaseClass {
  f = () => 2
}

class SubClass extends BaseClass {
  f() {} // Doesn't work - this won't shadow f() from the parent class
  f = () => super.f() // Doesn't work. This overrides f() from the parent class, so you can't access it's super method.
}

If you're not yet able to use this syntax, you can always create these functions in your constructor, like this:

class AuthService {
  constructor() {
    this.loginWithEmailAndPassword = (email, password) => (
      { email, password }
    )
  }
}

const authService = new AuthService()
console.log(authService.loginWithEmailAndPassword('x@y', 'Password!'))

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Implicit return in a javascript class method

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