SO answer 19121612

Context: SO answer 19121612 to SO question 19121574 https://stackoverflow.com/questions/19121574/jquery-validate-form

by Christian Heinrichs

HTML

<form action="" method="post" id="the_form">
  <input type='file' name="photosubmit" id="photosubmit" /><br>
  <input type="submit" value="Click me!" />
</form>

JavaScript

$("#the_form").submit(function(event) {
  if ( $( "input:first" ).val() !== "" ) {
    alert("The file input is valid.");
    return;
  }

  alert("The file input is not valid.")
  event.preventDefault();
});