Main.js

import client from '../utils/client';

export default class Main extends React.Component {
  state = { posts: [] }

  componentWillMount() {
    const request = client();

    request.get(`${API_ROOT}posts`).then(response => {
      return response.data
    }).then(data => {
      this.setState({ posts: data })
    }).catch(error => {
      console.log('Error:', error)
    })
  }
  
}

Do something like request.then( api => api.get ...)