<!DOCTYPE html>
<html>
<body>
<form action="form_action.asp">
Select a file: <input type="file" id="myFile" name="usr_file">
<input type="submit">
</form>
<p>Click the "Try it" button to set the required property for the file upload field.</p>
<p><strong>Tip:</strong> Click the "Submit" button before and after you have clicked the "Try it" button, to see the effect.</p>
<button onclick="myFunction()">Try it</button>
<p id="demo"></p>
<script>
function myFunction() {
document.getElementById("myFile").required = true;
document.getElementById("demo").innerHTML = "The required property was set. A file in the file upload field must now be filled out before submitting the form.";
}
</script>
</body>
</html>