Header already sent

Dear All,

I have a problem with “Header already sent” with my plugin. I know the problem because of javascript code is in the plugin file as below:

<?php
…
?>
<script type=”text/javascript”>
$(document).ready(function() {

$(“#user_login”).blur(function() { // when focus out

$(“#message”).html(‘checking username…’); //before AJAX response
var form_data = {
action: ‘check_username’,
username: $(this).val()
};
$.ajax({
type: “POST”,
url: “<?php bloginfo(‘wpurl’); ?>/wp-content/plugins/sidebar-color/functions.php”,
data: form_data,
success: function(result) {
$(“#message”).html(result);
}
});

});
/*$(“#user_login”).focus();*/

});
</script>

This mean that I have some space after ?> tag. so it provide an error.
My question is : Do we have any way to embed javascript code in the plugin file?

Pleas guide me if you know how to fix this problem.

Thanks in advances.