devdocs/assets/javascripts/lib/ajax.js

// TODO: This file was created by bulk-decaffeinate.
// Sanity-check the conversion and remove this comment.
/*
 * decaffeinate suggestions:
 * DS102: Remove unnecessary code created because of implicit returns
 * DS205: Consider reworking code to avoid use of IIFEs
 * DS207: Consider shorter variations of null checks
 * DS208: Avoid top-level this
 * Full docs: https://github.com/decaffeinate/decaffeinate/blob/main/docs/suggestions.md
 */
const MIME_TYPES = {
  json: 'application/json',
  html: 'text/html'
};

this.ajax = function(options) {
  applyDefaults(options);
  serializeData(options);

  const xhr = new XMLHttpRequest();
  xhr.open(options.type, options.url, options.async);

  applyCallbacks(xhr, options);
  applyHeaders(xhr, options);

  xhr.send(options.data);

  if (options.async) {
    return {abort: abort.bind(undefined, xhr)};
  } else {
    return parseResponse(xhr, options);
  }
};

ajax.defaults = {
  async: true,
  dataType: 'json',
  timeout: 30,
  type: 'GET'
};
  // contentType
  // context
  // data
  // error
  // headers
  // progress
  // success
  // url

var applyDefaults = function(options) {
  for (var key in ajax.defaults) {
    if (options[key] == null) { options[key] = ajax.defaults[key]; }
  }
};

var serializeData = function(options) {
  if (!options.data) { return; }

  if (options.type === 'GET') {
    options.url += '?' + serializeParams(options.data);
    options.data = null;
  } else {
    options.data = serializeParams(options.data);
  }
};

var serializeParams = params => ((() => {
  const result = [];
  for (var key in params) {
    var value = params[key];
    result.push(`${encodeURIComponent(key)}=${encodeURIComponent(value)}`);
  }
  return result;
})()).join('&');

var applyCallbacks = function(xhr, options) {
  if (!options.async) { return; }

  xhr.timer = setTimeout(onTimeout.bind(undefined, xhr, options), options.timeout * 1000);
  if (options.progress) { xhr.onprogress = options.progress; }
  xhr.onreadystatechange = function() {
    if (xhr.readyState === 4) {
      clearTimeout(xhr.timer);
      onComplete(xhr, options);
    }
  };
};

var applyHeaders = function(xhr, options) {
  if (!options.headers) { options.headers = {}; }

  if (options.contentType) {
    options.headers['Content-Type'] = options.contentType;
  }

  if (!options.headers['Content-Type'] && options.data && (options.type !== 'GET')) {
    options.headers['Content-Type'] = 'application/x-www-form-urlencoded';
  }

  if (options.dataType) {
    options.headers['Accept'] = MIME_TYPES[options.dataType] || options.dataType;
  }

  for (var key in options.headers) {
    var value = options.headers[key];
    xhr.setRequestHeader(key, value);
  }
};

var onComplete = function(xhr, options) {
  if (200 <= xhr.status && xhr.status < 300) {
    let response;
    if ((response = parseResponse(xhr, options)) != null) {
      onSuccess(response, xhr, options);
    } else {
      onError('invalid', xhr, options);
    }
  } else {
    onError('error', xhr, options);
  }
};

var onSuccess = function(response, xhr, options) {
  if (options.success != null) {
    options.success.call(options.context, response, xhr, options);
  }
};

var onError = function(type, xhr, options) {
  if (options.error != null) {
    options.error.call(options.context, type, xhr, options);
  }
};

var onTimeout = function(xhr, options) {
  xhr.abort();
  onError('timeout', xhr, options);
};

var abort = function(xhr) {
  clearTimeout(xhr.timer);
  xhr.onreadystatechange = null;
  xhr.abort();
};

var parseResponse = function(xhr, options) {
  if (options.dataType === 'json') {
    return parseJSON(xhr.responseText);
  } else {
    return xhr.responseText;
  }
};

var parseJSON = function(json) {
  try { return JSON.parse(json); } catch (error) {}
};