Using a PHP variable inside JavaScript

Question

I'm pretty new, so go easy. I am using a session in PHP with a few variables. I want to concatenate two strings together from my PHP session when the clicks a button. I am using JavaScript onclick to try and achieve this.

I am having trouble getting my JavaScript to accept my PHP variables. Does anybody have any suggestions?

PHP:

$_SESSION['user1'] = $_POST['user'];
$_SESSION['string3'] = $_POST['string1'];
$_SESSION['string4'] = $_POST['string2'];

echo $_SESSION['user1'];
echo $_SESSION['string3'];
echo $_SESSION['string4'];

if(isset($_SESSION['user1'])) {
    echo 'Welcome, '.$_SESSION['user1'].". Lets concatenate ".$_SESSION['string3']." and ".$_SESSION['string4'];

} else {
    echo "<meta http-equiv=\"refresh\" content=\"0;URL=">";
}


<button onclick="xy()">Try it</button>
<p id="answer"></p>

JS:

<script type="text/javascript">
function xy() {
    var x = "<?php $_SESSION['string3']; ?>";
    var y = "<?php $_SESSION['string4']; ?>";
    document.getElementById("answer").innerHTML = x + y;
}
</script>

echo "<meta http-equiv=\"refresh\" content=\"0;URL=">"; has an unescaped quote. — dave
– dave, Commented Jul 31, 2014 at 22:12

Shomz · Accepted Answer · 2014-07-31 22:21:16Z

4

You need to echo the PHP variable there because otherwise they output nothing and the JS variable ends up empty:

var x = "<?php echo $_SESSION['string3']; ?>";
var y = "<?php echo $_SESSION['string4']; ?>";

So for example, if $_SESSION['string3'] is "abc", PHP will echo the value inside the JS and you'll get this:

var x = "abc";

instead of:

var x = ""; // no output from PHP when there's no echo

To simplify things, here is your whole function:

<script type="text/javascript">
function xy() {
    var x = "<?php echo $_SESSION['string3']; ?>";
    var y = "<?php echo $_SESSION['string4']; ?>";
    document.getElementById("answer").innerHTML = x + y;
}
</script>

edited Jul 31, 2014 at 22:21

answered Jul 31, 2014 at 22:12

Shomz

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6 Comments

boxmein Over a year ago

Ah, sadly I was too slow to post a full answer, so I'll extend this one. There's a shorthand for equivalent behavior: <?= $_SESSION['string3']; ?>

Shomz Over a year ago

@boxmein I wrote it, and then decided to remove it because OP seems new to all this and didn't want to confuse him further. But yes, it's worth mentioning, thank you. :)

user3670475 Over a year ago

Where should I echo the PHP variable inside the JS function xy()?

Shomz Over a year ago

No, no, just once for x and once for y and that's it... From there, JS 'knows' the new values and you don't need to echo them from PHP again. I've updated my answer to show you the whole function.

user3670475 Over a year ago

@Shomz I updated the JS code as shown above. Nothing happens when I click the button. Am I missing something else?

|

NoNeedInName · Accepted Answer · 2014-07-31 22:16:45Z

0

Maybe it should be something like this?

echo "<script type=\"text/javascript\">\n";
echo "function xy() {\n";
echo "var x = ".$_SESSION['string3']."\";\n";
echo "var y = ".$_SESSION['string4']."\";\n";
echo "document.getElementById(\"answer\").innerHTML = x + y;\n}";
echo "</script>";

answered Jul 31, 2014 at 22:16

NoNeedInName

1

2 Comments

Shomz Over a year ago

Why would you do that?

NoNeedInName Over a year ago

@Shomz Just in case if the page was fully generated by PHP.

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