how to manage in JavaScript null values from PHP code -

i have next php/html code upload image:

<label>image (*)</label> <!-- if image exists, show --> <?php if($category->getimage() === null) : ?>     <input type="file" name="image" id="image" required> <?php else : ?>     <p><img src="../uploads/images/<?php echo $categoria->getimage(); ?>"></p>     <input type="file" name="image" id="image"> <?php endif; ?> 

and want validate using javascript

// validate image image = document.getelementbyid("image").value; if (!image) {     window.alert("you must select file image.");     document.getelementbyid("image").focus();     return false; } 

the image required. if create new registry sets of atributes null, including image. then, image not show , can set in form. if want update them, form shows current imagen don't have update if don't want to.

i need validate if file hasn't been uploaded , value null means user creating new registry , image required. if file hasn't been uploaded value isn't null, user updating registry , isn't required upload image.

thanks in advance , sorry bad english.

you can add id image

<img id="foo" src="../uploads/images/<?php echo $categoria->getimage(); ?>"> 

and check if it's in dom:

if ($('#foo').length) {     // image there } 

or without jquery:

if (document.getelementbyid("foo")) {     // image there }