How add svg in my custom visual???

Hello!

I want to add a svg in my custom visual. In all example i saw:

 public init(options:VisualInitOptions):void {

         var svg =this.svg=d3.select(options.element.get(0)).append('svg').classed('thermometer', true);

          ....

}

but... I don't have init method in my class. I have

constructor(options: VisualConstructorOptions) {... }

Yhank you for any help.