small filesize graphql request, returns promise

graphQlRequest.js

/**
 * small graphql request that adheres to the POST JSON spec, returns promise
 * @param {string} endpoint graphql url
 * @param {string} query graphql query / mutation
 * @param {object=} variables object of variables, optional
 * @param {object=} headers object of headers, optional
 * @return {Promise.<object, Error>} promise with json data
 * @example
    graphQlRequest('https://domain/endpoint', 'query { hero { name } }')
 */
const graphQlRequest = (endpoint, query, variables, headers = { 'content-type': 'application/json' }) => {
  const body = JSON.stringify({
    query,
    variables
  })

  const generateError = (msg = 'Server Response Error') => {
    throw new Error(msg)
  }

  return fetch(endpoint, { method: 'post', headers, body })
    .catch(() => generateError('Request Error'))
    .then(res => res.json().catch(() => generateError()))
    .then(res => {
      if (res.errors || typeof res.data !== 'object') {
        generateError(res.errors ? res.errors[0].message : undefined)
      }

      return res.data
    })
}

export default graphQlRequest