Then is not a function when method returns nothing - Javascript

Question

I'm trying to create a method, and in another method to access its return. However, when I don't return anything, the promise gives the error: then is not a function.

verifyUser() {
  if (currentUser.Title) {
    return Promise.resolve(currentUser)
  }
}

myMethod() {
  this.verifyUser
    .then(user => {
      console.log(user);
    })
}

When nothing returns, I tried to catch it, but it didn't work either

Does that not make sense? Undefined isn't a promise, it doesn't have then or catch props. — jonrsharpe
– jonrsharpe, Commented Apr 6, 2020 at 18:22
However, when I don't return anything, the promise gives the error: then is not a function. Which promise? When you don't return anything, there is no promise to call then on. — tkausl
– tkausl, Commented Apr 6, 2020 at 18:22
What should verifyUser do in the case when currentUser does not have Title. Throw an error, return null, … ? — t.niese
– t.niese, Commented Apr 6, 2020 at 18:22
in verifyUser, if you don't go inside the IF, the function does not return anything... Please, rewrite your code — Pierre
– Pierre, Commented Apr 6, 2020 at 18:23

MohammadAmin Mohammadi · Accepted Answer · 2020-04-06 18:36:09Z

2

The correct version of your code should be something like this:

function verifyUser() {
  return new Promise((resolve, reject) => {
    if (currentUser.Title) {
      resolve(currentUser);
    } else{
      reject();
    }
  });
}

function myMethod() {
  verifyUser()
    .then(user => {
      console.log(user);
    })
    .catch(() => {});
}

answered Apr 6, 2020 at 18:36

MohammadAmin Mohammadi

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3 Comments

Bergi Over a year ago

Using Promise.resolve() and Promise.reject() would be better though

jfriend00 Over a year ago

If verifyUser() has no async code, then why even use a promise at all?

MohammadAmin Mohammadi Over a year ago

No, but It's just a brief version! and show the main code structure. assuming there is lots of works to do in methods ...

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