<form class="upload-form">
<input class="upload-file" data-max-size="2048" type="file" >
<input type=submit>
</form>
<script>
$(function(){
var fileInput = $('.upload-file');
var maxSize = fileInput.data('max-size');
$('.upload-form').submit(function(e){
if(fileInput.get(0).files.length){
var fileSize = fileInput.get(0).files[0].size; // in bytes
if(fileSize>maxSize){
alert('file size is more then' + maxSize + ' bytes');
return false;
}else{
alert('file size is correct- '+fileSize+' bytes');
}
}else{
alert('choose file, please');
return false;
}
});
});
</script>
http://jsfiddle.net/9bhcB/2/