Got an error when tried to add new element into array state in React

Question

I am new to React and wanted to add new data into array state but faced an error:

Expected an assignment or function call and instead saw an expression

 getTitle(title) {
    axios
      .get(
        `http://api.openweathermap.org/data/2.5/forecast?q=${title}&APPID=7ad09d078633b652ecef8587a337639e&units=metric`
      )
      .then(res => {
        // this.setState({ title: res.data.city });
        this.setState(prevState => {
          title: [...prevState.title, res.data.list]; //Here I get the error
        });
      });
  }

Answer 1

setState needs to return an object representing the new state. Quickest fix is to wrap the body of that arrow function in parentheses:

this.setState(prevState => ({
  title: [...prevState.title, res.data.list],
}));

Now it's returning a json object

Answer 2

I think you forgot to return, try this:

this.setState(prevState => ({
    title: [...prevState.title, res.data.list] //Here I get the error
}))