angular2/atscript/src/change_detection/pipes/null_pipe.js

Angular 2 - a web framework for modern web apps

import {isBlank} from 'angular2/src/facade/lang';
import {Pipe, NO_CHANGE} from './pipe';

/**
 * @exportedAs angular2/pipes
 */
export class NullPipeFactory {
  supports(obj):boolean {
    return NullPipe.supportsObj(obj);
  }

  create(cdRef):Pipe {
    return new NullPipe();
  }
}

/**
 * @exportedAs angular2/pipes
 */
export class NullPipe extends Pipe {
  called:boolean;
  constructor() {
    super();
    this.called = false;
  }

  static supportsObj(obj):boolean {
    return isBlank(obj);
  }

  supports(obj) {
    return NullPipe.supportsObj(obj);
  }

  transform(value) {
    if (! this.called) {
      this.called = true;
      return null;
    } else {
      return NO_CHANGE;
    }
  }
}