问如何将angular 2+中的映射从html模板传递到自定义指令？

EN

<canvas id="seatsCanvasMain" 
        name="seatsCanvasMain" 
        appTheaterMap [takenSeatsMap]="show.theaterMap" 
        style="border:1px solid black">
</canvas>

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

@Directive({
  selector: '[appTheaterMap]'
})
export class TheaterMapDirective {
  canvas;
  @Input() takenSeatsMap: any;


  constructor(private el: ElementRef) {
    this.canvas = this.el.nativeElement;
  }

  ngOnInit() {

    this.canvas.onclick = (e) => {
      console.log(this.takenSeatsMap);//this will console log the map as an object. at first it seems that it passed correctly
      this.takenSeatsMap.get('4-4'); // ERROR TypeError: _this.takenSeatsMap.get is not a function

    }

  }

}