DOM not modified by var

why my DOM is not modified by this.tempo ?

public temporizador(){
    var counter = 0;
    var timer = setInterval(function() {
    if( counter >= 10 ) {
      clearInterval( timer );
    }

    this.tempo = counter;
    console.log(this.tempo);
    console.log( counter);
    counter++;
    }, 1000);
  }