AngularJS decorator to prevent identical request

duplicate-requests.decorator.js

const $duplicateRequestDecorator = ($delegate, $q) => {
  const pendingRequestPromises = {}

  function $http(config) {
    if (config.ignoreDuplicateRequest) {
      return $delegate(config)
    }

    let identifier = getRequestIdentifier(config)

    if (pendingRequestPromises[identifier]) {
      if (config.rejectDuplicateRequest) {
        return $q.reject({
          data: '',
          headers: {},
          status: config.rejectDuplicateStatusCode || 400,
          config: config,
        })
      }
      return $q.defer().promise
    }

    pendingRequestPromises[identifier] = $delegate(config).finally(() => {
      delete pendingRequestPromises[identifier]
    })

    return pendingRequestPromises[identifier]
  }

  Object.keys($delegate)
    .filter(key => angular.isFunction($delegate[key]))
    .forEach(key => ($http[key] = $delegate[key]))

  return $http
}

function hash(string) {
  let hash = 0
  if (string.length === 0) return hash
  for (let i = 0, charCode; i < string.length; ++i) {
    charCode = string.charCodeAt(i)
    hash = (hash << 5) - hash + charCode
    hash = hash & hash
  }
  return hash >>> 0
}

function getRequestIdentifier(config) {
  let string = config.method + config.url
  if (angular.isObject(config.params)) {
    string += angular.toJson(config.params)
  }
  if (angular.isObject(config.data)) {
    string += angular.toJson(config.data)
  }
  return hash(string)
}

$duplicateRequestDecorator.$inject = ['$delegate', '$q']
angular.module('shared').decorator('$http', $duplicateRequestDecorator)