event listeners javascript code example

Example 1: js eventlistener to add and remove stylings

const form = document.querySelector('form');
const fname = document.getElementById('fname');
const lname = document.getElementById('lname');
const para = document.querySelector('p');

form.onsubmit = function(e) {
  if (fname.value === '' || lname.value === '') {
    e.preventDefault();
    para.textContent = 'You need to fill in both names!';
  }
}

Example 2: event listener function called parameters

var someEventHander=function(event,param1,param2){
	console.log(event,param1,param2);
}
//add listener
document.getElementById("someid").addEventListener('click',someEventHander.bind(event,'param1','param2'), false);