fetchUser.js

 fetchUser(page) {
   //stackexchange User API url
    const url = `https://api.stackexchange.com/2.2/users?page=${page}&order=desc&sort=reputation&site=stackoverflow`;
    this.setState({ loading: true })
    axios.get(url)
      .then(res => {
        let listData = this.state.data;
        let data = listData.concat(res.data.items) . //concate list with response
        this.setState({ loading: false, data: data })
      })
      .catch(error => {
        this.setState({ loading: false, error: 'Something just went wrong' })
      });
  }