Javascript event listener on all class

  const divs = document.querySelectorAll('.hitung');

or

 const divs = document.querySelector('button[type="submit"]');

divs.forEach(el => el.addEventListener('keyup', event => {

var fm=el.form;

fm['a[harga1]'].value=fm["a[bruto]"].value - (fm["a[diskon1]"].value * fm["a[bruto]"].value / 100);

fm['a[harga2]'].value=fm["a[harga1]"].value - (fm["a[diskon2]"].value * fm["a[harga1]"].value / 100);

fm['a[harga3]'].value=fm["a[harga2]"].value - (fm["a[diskon3]"].value * fm["a[harga2]"].value / 100);

fm['a[harga]'].value=fm['a[harga3]'].value;

event.preventDefault();

  //console.log(event.target.classList[1]);

}));