transform(value: string, args: any[] = null): string {
   if (isBlank(value)) return value;
   if (!isString(value)) {
     throw new InvalidPipeArgumentException(LowerCasePipe, value);
   }
   return StringWrapper.toLowerCase(value);
 }

export function normalizeMethodName(method): RequestMethods {
  if (isString(method)) {
    var originalMethod = method;
    method = method.replace(/(\w)(\w*)/g, (g0, g1, g2) => g1.toUpperCase() + g2.toLowerCase());
    method = RequestMethods[method];
    if (typeof method !== 'number')
      throw makeTypeError(
          `Invalid request method. The method "${originalMethod}" is not supported.`);
  }
  return method;
}

 /**
  * Performs any type of http request. First argument is required, and can either be a url or
  * a {@link Request} instance. If the first argument is a url, an optional {@link RequestOptions}
  * object can be provided as the 2nd argument. The options object will be merged with the values
  * of {@link BaseRequestOptions} before performing the request.
  */
 request(url: string | Request, options?: RequestOptionsArgs): any {
   var responseObservable: any;
   if (isString(url)) {
     responseObservable = httpRequest(
         this._backend,
         new Request(mergeOptions(this._defaultOptions, options, RequestMethods.Get, url)));
   } else if (url instanceof Request) {
     responseObservable = httpRequest(this._backend, url);
   } else {
     throw makeTypeError('First argument must be a url string or Request instance.');
   }
   return responseObservable;
 }

 transform(value: any, args: any[] = null): any {
   if (isBlank(args) || args.length == 0) {
     throw new BaseException('Slice pipe requires one argument');
   }
   if (!this.supports(value)) {
     throw new InvalidPipeArgumentException(SlicePipe, value);
   }
   if (isBlank(value)) return value;
   var start: number = args[0];
   var end: number = args.length > 1 ? args[1] : null;
   if (isString(value)) {
     return StringWrapper.slice(value, start, end);
   }
   return ListWrapper.slice(value, start, end);
 }

 /**
  * whether this is querying for a variable binding or a directive.
  */
 get isVarBindingQuery(): boolean { return isString(this.selector); }

 var stringifiedKeys = keys.map(k => isString(k) ? `"${k}"` : `${k}`).join(', ');

 private supports(obj: any): boolean { return isString(obj) || isArray(obj); }

 ListWrapper.join(ListWrapper.map(keys, (k) => isString(k) ? `"${k}"` : `${k}`), ", ");