code: function enableContentTypeShortcut() {
              var CONTENT_TYPE_ALIAS = {
                  json: 'application/json'
              };
  
              // 自动转换`contentType`
              ajax.hooks.beforeExecute = function (options) {
                  if (options.contentType &&
                      CONTENT_TYPE_ALIAS.hasOwnProperty(options.contentType)
                  ) {
                      options.contentType =
                          CONTENT_TYPE_ALIAS[options.contentType];
                  }
              };
          }
docs: 开启`contentType`属性简写功能
  
  @ignore