angular 2 typescript 无法在环境上下文中声明实现

我是typescript新手，我正在try 为angular 2指令创建一个函数.

无法在环境上下文中声明实现

该消息适用于offset()和toggler().

import { Directive, ElementRef, Input } from '@angular/core';

@Directive({
  selector: 'offCanvas',
  inputs: ['target', 'toggle', 'placement', 'autohide', 'recalc', 'disableScrolling', 'modal', 'canvas', 'exclude'],
  host: {
    '(click)': 'Click()'
  }
})

export class OffCanvas {  
  @Input('target') target: string;
  @Input('canvas') canvas: string;
  @Input('state') state: string;
  @Input('exclude') exclude: string;
  @Input('placement') placement: string;
  @Input('toggle') toggle: boolean;
  @Input('autohide') autohide: boolean;
  @Input('recalc') recalc: boolean;
  @Input('disableScrolling') disableScrolling: boolean;
  @Input('modal') modal: boolean;

  public offset() {
    switch (this.placement) {
      case 'left':
      case 'right':  return (<HTMLElement>document.querySelector(this.target)).offsetWidth
      case 'top':
      case 'bottom': return (<HTMLElement>document.querySelector(this.target)).offsetHeight
    }
  }

  public toggler() {
    if (this.state === 'slide-in' || this.state === 'slide-out') return
    this[this.state === 'slid' ? 'hide' : 'show']()
  }

  Click() {
    this.toggler()
  }
}