Onclick does nothing

Useful thanks, understand more now about server(php)/client(js). I tried below, which adds a row when the page loads, but not with onclick. Dunno how to use js to send a request to php, which should be simple even for novice.

<script>
function add_row() {
<?php $this->table_model->add_row( 'file.doc' ); ?>
}
</script>

<a href="http://downloadfiles.com/file.doc" onclick="add_row()">