How to add dropdown dynamically - php

Question

I am trying to add the dynamic drop down through javascript.
i have a dropdown which has numbers, when selected creates the drop down.
but i want to add the dynamic dropdown through javascript.
how can i do this?
here is php code
code:
<?php
try {
$dbh = new PDO('mysql:dbname=theaterdb;host=localhost','tiger','tiger');
} catch (PDOException $e) {
echo 'Connection failed: ' . $e->getMessage();
}
$sql = "SELECT theater_name FROM theater;";
$sth = $dbh->prepare($sql);
$sth->execute();
echo "<select name='theater_name' id='course' onchange='showUser(this.value);'>";
echo "<option>----Select Theater----</option>";
while($row = $sth->fetch(PDO::FETCH_ASSOC)) {
echo "<option value='" . $row['theater_name'] ."'>" . $row['theater_name']. "</option>";
}
echo "</select>";
?>
This php code gets the drop down values from mysql database.
but this drop down will be created dynamically from javascript
javascript code
function create(param) {
'use strict';
var i, target = document.getElementById('screens');
target.innerHTML = '';
for(i = 0; i < param; i += 1) {
target.innerHTML +='</br>';
target.innerHTML +='Movie in hall '+i+' ';
target.innerHTML += '<?php
try {
$dbh = new PDO('mysql:dbname=theaterdb;host=localhost','tiger','tiger');
} catch (PDOException $e) {
echo 'Connection failed: ' . $e->getMessage();
}
$sql = "SELECT theater_name FROM theater;";
$sth = $dbh->prepare($sql);
$sth->execute();
echo "<select name='theater_name' id='course' onchange='showUser(this.value);'>";
echo "<option>----Select Theater----</option>";
while($row = $sth->fetch(PDO::FETCH_ASSOC)) {
echo "<option value='" . $row['theater_name'] ."'>" . $row['theater_name']. "</option>";
}
echo "</select>";
?>';
target.innerHTML +=' '+'Timings '+' ';
target.innerHTML += '<input type="text" name="timings">';
target.innerHTML +='</br>';
target.innerHTML +='</br>';
}
}
so now i have added this php code in javascript but it is not creating the dropdown..
Why? How can i do this

Answer 1

You are using PHP to generate JavaScript as the JavaScript is interpreted by the browser and PHP is processed by the server the code below will not work
target.innerHTML += '<?php'; ...
For you to understand the process is as follows,
Server reads and processes the php
The server generates the HTML from php
The JavaScript that is contained in the HTML is interpreted by the browser
what you can do is pass data to javascript, and generate the dropdown.
or if you need information from the User (as parameters) to generate the dropdown, you can make a request by ajax.
the link explain about the ajax with dropdown -> http://imasters.com.br/artigo/3918/javascript/ajax-e-php-carregando-dados-sem-refresh/

Answer 2

This is a string delimiter problem. You are using single quotes ' for your javascript string in
target.innerHTML += '<?php
so the string is supposed to end at the first next single quote, that is the first echoed in this line:
echo "<select name='theater_name' id='course' onchange='showUser(this.value);'>";
Javascript interpreter ends the string in ...<select name=. There is no operator or ; after that, (there is the character t) and it stucks.
You should just add a backslash \ in front of each single quote, as an escape:
echo "<select name=\'theater_name\' id=\'course\' onchange=\'showUser(this.value);\'>";
Or you can substitute the string delimiter for your echo, using the same delimiter for both javascript and php like:
echo '<select name="theater_name" id="course" onchange="showUser(this.value);">';
The same occurs in the third echo, in while.
There is some difference in PHP while using single ' or double quote " as a string delimiter: double quoted strings have more escape sequences and do expand variables. Please refer to PHP docs while making your choice. Any choice has no consequences in your script.