I am building a simple movie catalogue using themoviedb API however I am facing an issue that I am unable to solve. The issue is that the result after fetching is always undefined.

I tried with the method componentWillMount to fetching data and the setting the state inside this method but it does not work. I tried to fetch inside constructor, no result.

This is my code so far

import React, { Component } from 'react';
import Header from './components/Header';
import MovieList from './components/MovieList';
import Footer from './components/Footer';

const MOVIE_API = "http://api.themoviedb.org/3/discover/movie?api_key=72049b7019c79f226fad8eec6e1ee889&language=en-US&sort_by=release_date.desc&include_adult=true&include_video=false&page=2&primary_release_year=2018";

//class
class App extends Component {
  constructor(props){
    super(props);

    this.state = {
      movies: [],
      movieName: ''
    }
  }


  componentWillMount(){
    this.fetchMovie();
  }


//fetching movie
  fetchMovie = () =>{
    const req = new Request(MOVIE_API, {
      method: 'GET',
      cache: 'default'
    });

    fetch(req).then(response =>{
      return response.json();
    }).then(data =>{
      console.log(data); //REF 1;
      this.setState({
        movies: data
      });
    }).catch(err => {
      console.log("ERROR: " + err);
    })
  }

  render() {
    return (
      <div className="root">
        <Header />
        <MovieList moviesRes={this.state.movies}/>
        <Footer />

      </div>
    );
  }
}

export default App;

As you can see I called the method componentWillMount to fetch the data but it does not work. It is also noticeable that if I log the data (REF 1) I can see the result (json).

===========================

EDIT

This is the code for MovieList

/*import React, { Component } from 'react';

export default class MovieList extends Component{
    constructor(props){
        super(props);
        this.state = {
            movies: this.props.movieRes
        }
    }
    render(){

        //if result is undefined 
        if(this.state.movieRes === undefined){
            return(
                <h1>Loading...</h1>
            );
        }else{
            return(
                <ul>
                {this.state.movieRes.map((movie, index)=>{
                    return (
                        <li key={index}>{movie.title}</li>
                    );
                })}
                </ul>
            );
        }
    }
}*/

=================

update child code

import React, { Component } from 'react';

export default class MovieList extends Component{

    render(){
        const { movieRes = [] } = this.props; // we are assigning a default prop here of an empty array.
        return(
            <ul>
                {
                    //return movie from array
                    movieRes.map((movie, index)=>{
                        return (
                            <li key={index}>
                                {movie.id}
                            </li>
                        );
                    })
                }
            </ul>
        );
    }
}

In this I way I suppress the error, but still it is not working. From what I learnt, React should render as soon as it detect changes but for some reason it not the case.

IMAGE

As you can see from the image when I am passing the array from parent component to the child component the array length is 20 but in the child component the array length seems to be 0

===================

Solution

I changed the component from class to a const and pass to it the array and everything went smooth. Here is the final code:

import React from 'react';

const MovieList = ({movies}) =>{
    if(!movies){
        return <h1>Loading...</h1>
    }
    return (
        <ul>
            {
                movies.map((movie, index) => {
                    return (
                        <li key={index}>
                            <p>{movie.title}</p>
                        </li>
                    )
                })
            }
        </ul>
    );

}

export default MovieList;