How to use the fullcalendar.applyAll function in fullcalendar

rawEventDefs = this.gcalItemsToRawEventDefs(
            res.body.items,
            requestParams.timeZone
          )
        }

        if (rawEventDefs) {
          let callbackRes = applyAll(ajaxSettings.success, null, [ rawEventDefs, res ])

          if (Array.isArray(callbackRes)) {
            rawEventDefs = callbackRes
          }

          onSuccess(this.parseEventDefs(rawEventDefs))
        } else {
          applyAll(ajaxSettings.error, null, [ error, res ])
          onFailure()
        }
      })
  }

this.calendar.popLoading()

        if (res && res.body && res.body.error) {
          this.reportError('Google Calendar API: ' + res.body.error.message, res.body.error.errors)
        } else if (error) {
          this.reportError('Google Calendar API', error)
        } else {
          rawEventDefs = this.gcalItemsToRawEventDefs(
            res.body.items,
            requestParams.timeZone
          )
        }

        if (rawEventDefs) {
          let callbackRes = applyAll(ajaxSettings.success, null, [ rawEventDefs, res ])

          if (Array.isArray(callbackRes)) {
            rawEventDefs = callbackRes
          }

          onSuccess(this.parseEventDefs(rawEventDefs))
        } else {
          applyAll(ajaxSettings.error, null, [ error, res ])
          onFailure()
        }
      })
  }