Flow - How to setState with a value I get from a function?

Question

In the getEvaluation function I get the number 1, I want to change the state with this value:

type Props = {
};

type State = {
    id_evaluation: string,
};

class Evaluation extends Component < Props, State > {
    state = {
        id_evaluation: '1',
    }

    componentDidMount() {
        const id_eval = getEvaluation();

        this.setState({
            id_evaluation: id_eval,
        });

I checked now 'console.log(typeof(id_eval)), is string.

Flow generates this error:

Cannot call this.setState with object literal bound to partialState because null or undefined [1] is incompatible with string [2].

Answer 1

Try to convert id_eval into a string like this.

type Props = {
};

type State = {
    id_evaluation: string,
};

class Evaluation extends Component < Props, State > {
    state = {
        id_evaluation: '1',
    }

    componentDidMount() {
        const id_eval = getEvaluation();

        this.setState({
            id_evaluation: String(id_eval) || '',
        });

Answer 2

How about this one:

state = {
  id_evaluation: 1,
};

const id_eval = getEvaluation();
this.setState({
   id_evaluation: id_eval,
});

Answer 3

The return value of the getEvaluation() function has a variety of cases, Number type, Null type or Undefined type, but your State limit accepts the String type, which is the error reported in the compilation phase, you need to convert the return value of getEvaluation(), for example using String(id_eval).