javascript add/remove class on click

js:

document.querySelector('.target').addEventListener('click', function(event) {

  event.preventDefault();

  var target = document.querySelector('.target');

  if (target.classList.contains('active')) {

    target.classList.remove('active');

  } else {

    target.classList.add('active');

  }

});

html:

<button class="target">click to add/remove class</button>