<!DOCTYPE html>
<html>
<body>
First Name: <input type="text" id="myText" value="Mickey">
<p>Click the button to change the default value of the text field.</p>
<button type="button" onclick="myFunction()">Try it</button>
<script>
function myFunction() {
document.getElementById("myText").defaultValue = "Goofy";
}
</script>
</body>
</html>