document.getElementById('id').selectedIndex does not read the index but the code itself as string

Question

i have a JavaScript here embedded in a PHP script "echo". when i use the document.getElementById('list_subjects').selectedIndex in alert box it gives the result but when i use it in a php array variable. it says undefined index. i did (int)$index to convert it a integer but its output only is always zero. whats the problem here? Thank You!

<?php

echo "<script> function subject_name(){" . ($index = "(document.getElementById('list_subjects').selectedIndex)") . ";document.getElementById('subj_name').innerHTML = '" . ($list_options_name[(int)$index]) . "';} </script>";

?>

Answer 1

$index = "(document.getElementById('list_subjects').selectedIndex"

The above line will NOT store the selectedIndex in the value of $index, PHP is a server-side scripting language and JS is client side. The above line is invalid.

The values should be accessed/passed using a ajax call.

Tutorial : http://www.w3schools.com/ajax/