window.fetch = function()

in packages/rum-core/src/common/patching/fetch-patch.js [73:146]
66 lines of code
8 McCabe index (conditional complexity)

  window.fetch = function (input, init) {
    var fetchSelf = this
    var args = arguments
    var request, url
    var isURL = input instanceof URL
    if (typeof input === 'string' || isURL) {
      request = new Request(input, init)
      if (isURL) {
        url = request.url
      } else {
        // when the input is a string, the url value should be copied from it, rather than from request.url
        // this is important, there are existing users using relative urls when using fetch, which generates a span.name like 'GET /path-example'
        // switching to request.url like we do now with the introduction of URL objects support would start changing existing spans
        // the name would start being something like 'GET http://the-url-of-the-web-page.tld/path-example' which would cause unexpected results in the Kibana side
        url = input
      }
    } else if (input) {
      request = input
      url = request.url
    } else {
      return nativeFetch.apply(fetchSelf, args)
    }

    const task = {
      source: FETCH,
      state: '',
      type: 'macroTask',
      data: {
        target: request,
        method: request.method,
        url,
        aborted: false
      }
    }

    return new Promise(function (resolve, reject) {
      globalState.fetchInProgress = true
      scheduleTask(task)
      var promise
      try {
        promise = nativeFetch.apply(fetchSelf, [request])
      } catch (error) {
        reject(error)
        task.data.error = error
        invokeTask(task)
        globalState.fetchInProgress = false
        return
      }

      promise.then(
        response => {
          let clonedResponse = response.clone ? response.clone() : {}
          resolve(response)
          // invokeTask in the next execution cycle to let the promise resolution complete
          scheduleMicroTask(() => {
            task.data.response = response
            const { body } = clonedResponse
            if (body) {
              readStream(body, task)
            } else {
              invokeTask(task)
            }
          })
        },
        error => {
          reject(error)
          scheduleMicroTask(() => {
            handleResponseError(task, error)
          })
        }
      )
      globalState.fetchInProgress = false
    })
  }