Fetch JSON using Promisified XMLHttpRequest

fetch-json.js

export default function fetchJson(url) {
  return new Promise((resolve, reject) => {
    const request = new XMLHttpRequest()
    request.open('GET', url, true)
    request.setRequestHeader('Accept', 'application/json')
    request.onload = function() {
      if (request.status >= 200 && request.status < 400) {
        try {
          const json = JSON.parse(request.responseText)
          resolve(json)
        } catch (err) {
          reject(new Error('Unable to convert response to JSON'))
        }
      } else {
        reject(request)
      }
    };
    request.onerror = function() {
      reject(request)
    }
    request.send()
  })
}