SO - 16765823

by Arun P Johny

HTML

<form method="post" enctype="multipart/form-data" action="">
    <label for="fname"> First Name: </label> <input  type="text" name="fname"  /> <br /><br />
    <label for="file"> Select File: </label> <input  type="file" id="file" />
    <input type="submit" name="submit" value="Submit" />
</form>

JavaScript

document.forms[0].addEventListener('submit', function( evt ) {
    var f = document.getElementById('file');
    var file = f.files ? f.files[0] : f;
    
    if(file && file.size < 18000) { 
        //Submit form
        alert('Size is valid');
    } else {
        alert('pic too big');
        evt.preventDefault();
    }
}, false);