How to prevent sending an empty field to the server?

Question

JavaScript

There is a comment attribute on the route object, for example. How to prohibit sending an empty, not filled, field to the Back? (despite the fact that the filled textarea needs to be sent, of course)
Angular || React || Native?
And that it at each sending there develops and clutters up a DB.

Answer 1

Turned out to be just = null

Answer 2

document.querySelector('#form').onsubmit = function(){
  if (!document.querySelector('#textarea').value) {
    return false;
  }     
}

or

document.querySelector('#form').onsubmit = function(event){
  if (!document.querySelector('#textarea').value) {
    event.preventDefault()
  }
}