Set custom message for required and field validation

<h4>Example custom message for required input fields</h4>
<p>Add some text in the input field and click Send.</p>

<form action='#' method='post'>
Email: <input type='email' id='email_1' required placeholder='Email address'/><br>
<input type='submit' value='Send'/>
</form>

<script>
var email_1 = document.querySelector('#email_1');

//register invalid event that shows a custom message on invalidated of the field
email_1.addEventListener('invalid', function(ev){
 ev.target.setCustomValidity('Your custom message');
});

//this is necessary to remove the invalidate mark on validated filed
email_1.addEventListener('input', function(ev){
 ev.target.setCustomValidity('');
});
</script>

<h4>Example emitting the invalid event</h4>
<p>For test, select a date lower then curent date.</p>

<input type='date' id='date1' required placeholder='Select a date'>

<script>
//function called by the change event
//receives the default event argument, a js object with target event
function dateActiv(ev){
 var elm = ev.target; //get the element from event
 var sel_date = new Date(elm.value);

 //if selected date is lower than current date
 if(sel_date <= new Date()){
 elm.value =''; //set empty to detect as not valid when invalid event is emitted
 elm.reportValidity(); //to emit invalid event
 }
}

//register change event that cals dateActiv()
document.querySelector('#date1').addEventListener('change', dateActiv);

//register invalid event that shows a custom message
document.querySelector('#date1').addEventListener('invalid', function(ev){
 if(ev.target.value =='' || ev.target.validity.typeMismatch) {
 ev.target.setCustomValidity('Your custom message');
 return false;
 }
 return true;
});
</script>