ReactJS: What is "Cannot read property 'then' of undefined"?

Question

I have two method calls within a function called loginUser(). The first passes in userInfo and makes an API request, and then would like to execute the method to empty out the login text fields.

But I am getting the error Cannot read property 'then' of undefined. What may be the issue?

Code:

  _loginUser() {
    this.props.loggingInUser(this.props.userInfo) //Would like to finish this first before moving onto calling this.props.emptyLoginTextFields()
    .then(() => { //Here is where the error is occurring
      this.props.emptyLoginTextFields()
    })
  }

Thank you in advance!

It sounds like either `props` or `loggingInUser()` is undefined, can you try logging out `props` or debugging and ensuring that both are defined? — Dave V, Oct 14 '16 at 19:55
Possible duplicate of [Detecting an undefined object property](http://stackoverflow.com/questions/27509/detecting-an-undefined-object-property) — Jared Smith, Oct 14 '16 at 21:46

score 4 · Answer 1 · answered Oct 14 '16 at 21:36

You need to return the the promise manager like "axios" that returns the results ,

example : focus on

"return axios.all"

 getPlayersInfo: function (players) {
    return axios.all(players.map((username) => {
        return getUserInfo(username)

    }))
        .then((info) => {
        return info.map((user) => {
            return user.data;
        });
    })
        .catch( function (err) {
        console.warn("error in getPlayerInfo",err);
    });
}

};

Thanks, I don't see "return" in other answer, but your answer save my day — Carlos Parada, Dec 07 '17 at 22:04

score 2 · Answer 2 · answered Apr 21 '20 at 16:40

2

In my case was, that I didn't have an axios mock.

So I created src/__mocks__/axios.js with this code:

export default {
    get: jest.fn().mockResolvedValue({ data: {} })
};

answered Apr 21 '20 at 16:40

Jöcker

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score 1 · Answer 3 · edited Oct 14 '16 at 22:27

1

Just be careful to return the promise from the ajax call inside of the loggingInUser function. You probably don't have a return statement in it and the default return value is undefined for JS.

An example:

function loggingInUser(credentials) {
  return fetch('/foo/bar');
}

edited Oct 14 '16 at 22:27

jannis

4,843
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answered Oct 14 '16 at 20:41

Stefan Turcanu

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ReactJS: What is "Cannot read property 'then' of undefined"?

3 Answers3