JSFiddle - React, Tailwind, and code Playground

HTML

<form id="myForm">
<input type="text" id="theInput" value="/script.php">
<button type="button" id="changeForm">Update Action</button>
</form>

JavaScript

(function(){
	document.getElementById('changeForm').onclick = function(e) {
    document.getElementById('myForm').action = document.getElementById('theInput').value;

    // reflecting change in console, inspect otherwise
    console.log('Form submit: ' + document.getElementById('myForm').action);
  }
})();