Helper function for Fetch API

api-helper.js

/**
 * Simple GET and POST functions that return Promise.
 * 
 * Example:
 *   myAPI.get( url ).then( result => { ... } );
 *   myAPI.post( url, data ).then( result => { ... } );
 */
export let myAPI = {
  get( endpoint ) {
    return window.fetch( endpoint, {
      method: 'GET',
      headers: { 'Accept': 'application/json' }
    } )
    .then( this._handleError )
    .then( this._handleContentType )
    .catch( this._throwError );
  },

  post( endpoint, body ) {
    return window.fetch( endpoint, {
      method: 'POST',
      headers: { 'content-type': 'application/json' },
      body: JSON.stringify( body ),
    } )
    .then( this._handleError )
    .then( this._handleContentType )
    .catch( this._throwError );
  },

  _handleError( err ) {
    return err.ok ? err : Promise.reject( err.statusText )
  },

  _handleContentType( res ) {
    const contentType = res.headers.get( 'content-type' );
    if( contentType && contentType.includes( 'application/json' ) ) {
      return res.json()
    }
    return Promise.reject( 'Oops, we haven\'t got JSON!' )
  },

  _throwError( err ) {
    throw new Error( err );
  }
};