change value after button clicked in html code example

Example 1: javascript change button text onclick

<!DOCTYPE html>
<html>
<body>

<button id="demo" onclick="myFunction()">Click me to change my HTML content (innerHTML).</button>

<script>
function myFunction() {
  document.getElementById("demo").innerHTML = "Paragraph changed!";
}
</script>

</body>
</html>

Example 2: how to change the text in a button on onclick

var btn = document.getElementById("mybtn");
btn.value = 'my value'; // will just add a hidden value
btn.innerHTML = 'my text';