set class code example

Example 1: js add class

var element = document.getElementById('element');
element.classList.add('class-1');
element.classList.add('class-2', 'class-3');
element.classList.remove('class-3');

Example 2: add classnames to body

openModal = (event) => {
  document.body.classList.add('modal-open');
  this.setState({ showModal: true });
}
hideModal = (event) => {
  document.body.classList.remove('modal-open');
  this.setState({ showModal: false });
}