How to Output JavaScript with PHP

How can I store JavaScript variable output into a PHP variable?

You have to remember that if JS and PHP live in the same document, the PHP will be executed first (at the server) and the JS will be executed second (at the browser)--and the two will NEVER interact (excepting where you output JS with PHP, which is not really an interaction between the two engines).

With that in mind, the closest you could come is to use a PHP variable in your JS:

<?php
$a = 'foo'; // $a now holds PHP string foo
?>
<script>
var a = '<?php echo $a; ?>'; //outputting string foo in context of JS
//must wrap in quotes so that it is still string foo when JS does execute
//when this DOES execute in the browser, PHP will have already completed all processing and exited
</script>
<?php
//do something else with $a
//JS still hasn't executed at this point
?>

As I stated, in this scenario the PHP (ALL of it) executes FIRST at the server, causing:

  1. a PHP variable $a to be created as string 'foo'
  2. the value of $a to be outputted in context of some JavaScript (which is not currently executing)
  3. more done with PHP's $a
  4. all output, including the JS with the var assignment, is sent to the browser.

As written, this results in the following being sent to the browser for execution (I removed the JS comments for clarity):

<script>
var a = 'foo';
</script>

Then, and only then, will the JS start executing with its own variable a set to "foo" (at which point PHP is out of the picture).

In other words, if the two live in the same document and no extra interaction with the server is performed, JS can NOT cause any effect in PHP. Furthermore, PHP is limited in its effect on JS to the simple ability to output some JS or something in context of JS.

How to output a javascript file from a PHP file that can be referenced from a script include tag

Put JavaScript Headers in PHP file

Keep your HTML page the same. Call it as a .php file:

<script type="text/javascript" src="javascriptHandler.php"></script>

In your javascriptHandler.php file, add this to the very top of the file:

<?php
header("Content-Type: application/javascript");
header("Cache-Control: max-age=604800, public");
?>

Then you can put your regular javascript below. All together it will look like:

<?php
header("Content-Type: application/javascript");
header("Cache-Control: max-age=604800, public");
?>

function bob(){
alert('hello')
}
bob();

and your browser will treat your javascriptHandler.php file like a JavaScript resource. Normal caching rules will apply.

How to print JavaScript with PHP

By doing it your way, it's just impossible. PHP can't "read" or "interact with" javascript directly in the same page.

You have to understand that PHP is a preprocessor, it generates HTML on the server, then the generated page is sent to the client. In this page, the PHP code has entirely disappeared. You can only see what it generated (that is, HTML or JS). Then, the javascript code runs, and it has no idea it was generated using PHP, and no idea of PHP's presence whatsoever.

In order to pass variables to a PHP script, you have to call the file with GET or POST methods :

(JS)

$.get( 'myScript.php', { // This is calling the PHP file, passing variables (use get or post)
variable1 : "Hello",
variable2 : "world!"
}, function(data){ // PHP will then send back the response as "data"
alert(data); // will alert "Hello world!"
});

(myScript.php)

    $variable1 = $_GET['variable1']; // or POST if you're using post
$variable2 = $_GET['variable2'];

echo $variable1 . " " . $variable2; // Concatenates as "Hello world!" and prints it out.
//The result of the PHP file is sent back to Javascript when it's done.

Of course, this is a very basic example. Never read and use directly what is sent to PHP (as I just did), because anyone could inject whatever they'd want. Add securities.

How to echo (or print) to the js console with php

<?php
echo '<script>console.log("Your stuff here")</script>';
?>

How do I pass variables and data from PHP to JavaScript?

There are actually several approaches to do this. Some require more overhead than others, and some are considered better than others.

In no particular order:

  1. Use AJAX to get the data you need from the server.
  2. Echo the data into the page somewhere, and use JavaScript to get the information from the DOM.
  3. Echo the data directly to JavaScript.

In this post, we'll examine each of the above methods, and see the pros and cons of each, as well as how to implement them.

1. Use AJAX to get the data you need from the server

This method is considered the best, because your server side and client side scripts are completely separate.

Pros

  • Better separation between layers - If tomorrow you stop using PHP, and want to move to a servlet, a REST API, or some other service, you don't have to change much of the JavaScript code.
  • More readable - JavaScript is JavaScript, PHP is PHP. Without mixing the two, you get more readable code on both languages.
  • Allows for asynchronous data transfer - Getting the information from PHP might be time/resources expensive. Sometimes you just don't want to wait for the information, load the page, and have the information reach whenever.
  • Data is not directly found on the markup - This means that your markup is kept clean of any additional data, and only JavaScript sees it.

Cons

  • Latency - AJAX creates an HTTP request, and HTTP requests are carried over network and have network latencies.
  • State - Data fetched via a separate HTTP request won't include any information from the HTTP request that fetched the HTML document. You may need this information (e.g., if the HTML document is generated in response to a form submission) and, if you do, will have to transfer it across somehow. If you have ruled out embedding the data in the page (which you have if you are using this technique) then that limits you to cookies/sessions which may be subject to race conditions.

Implementation Example

With AJAX, you need two pages, one is where PHP generates the output, and the second is where JavaScript gets that output:

get-data.php

/* Do some operation here, like talk to the database, the file-session
* The world beyond, limbo, the city of shimmers, and Canada.
*
* AJAX generally uses strings, but you can output JSON, HTML and XML as well.
* It all depends on the Content-type header that you send with your AJAX
* request. */

echo json_encode(42); // In the end, you need to echo the result.
// All data should be json_encode()d.

// You can json_encode() any value in PHP, arrays, strings,
//even objects.

index.php (or whatever the actual page is named like)

<!-- snip -->
<script>
function reqListener () {
console.log(this.responseText);
}

var oReq = new XMLHttpRequest(); // New request object
oReq.onload = function() {
// This is where you handle what to do with the response.
// The actual data is found on this.responseText
alert(this.responseText); // Will alert: 42
};
oReq.open("get", "get-data.php", true);
// ^ Don't block the rest of the execution.
// Don't wait until the request finishes to
// continue.
oReq.send();
</script>
<!-- snip -->

The above combination of the two files will alert 42 when the file finishes loading.

Some more reading material

  • Using XMLHttpRequest - MDN
  • XMLHttpRequest object reference - MDN
  • How do I return the response from an asynchronous call?

2. Echo the data into the page somewhere, and use JavaScript to get the information from the DOM

This method is less preferable to AJAX, but it still has its advantages. It's still relatively separated between PHP and JavaScript in a sense that there is no PHP directly in the JavaScript.

Pros

  • Fast - DOM operations are often quick, and you can store and access a lot of data relatively quickly.

Cons

  • Potentially Unsemantic Markup - Usually, what happens is that you use some sort of <input type=hidden> to store the information, because it's easier to get the information out of inputNode.value, but doing so means that you have a meaningless element in your HTML. HTML has the <meta> element for data about the document, and HTML 5 introduces data-* attributes for data specifically for reading with JavaScript that can be associated with particular elements.
  • Dirties up the Source - Data that PHP generates is outputted directly to the HTML source, meaning that you get a bigger and less focused HTML source.
  • Harder to get structured data - Structured data will have to be valid HTML, otherwise you'll have to escape and convert strings yourself.
  • Tightly couples PHP to your data logic - Because PHP is used in presentation, you can't separate the two cleanly.

Implementation Example

With this, the idea is to create some sort of element which will not be displayed to the user, but is visible to JavaScript.

index.php

<!-- snip -->
<div id="dom-target" style="display: none;">
<?php
$output = "42"; // Again, do some operation, get the output.
echo htmlspecialchars($output); /* You have to escape because the result
will not be valid HTML otherwise. */
?>
</div>
<script>
var div = document.getElementById("dom-target");
var myData = div.textContent;
</script>
<!-- snip -->

3. Echo the data directly to JavaScript

This is probably the easiest to understand.

Pros

  • Very easily implemented - It takes very little to implement this, and understand.
  • Does not dirty source - Variables are outputted directly to JavaScript, so the DOM is not affected.

Cons

  • Tightly couples PHP to your data logic - Because PHP is used in presentation, you can't separate the two cleanly.

Implementation Example

Implementation is relatively straightforward:

<!-- snip -->
<script>
var data = <?php echo json_encode("42", JSON_HEX_TAG); ?>; // Don't forget the extra semicolon!
</script>
<!-- snip -->

Good luck!

Live displaying PHP output on a webpage

Loading the script in an iframe should work.

<iframe src="/script.php"></iframe>

Or alternatively if you need it to load after a specific action

<iframe id='myIframe'></iframe>

<script type="text/javascript">
document.getElementById('myIframe').src = '/script.php';
<script>

How to output Javascript from PHP files with PHP variables embedded in JS code?

You could use a template engine to do this (such as Smarty for instance). Simply write your JS files using the template variables where your PHP variables would be, and load them through PHP.

You could even roll your own simple one. Something like:

// in JS file:
function myFunc() {
alert("hello %s");
}

// in PHP file:
<?PHP
//... code to open JS file and load into string....
echo sprintf($contentsOfJSFile, "John Doe");
?>

RESULTING OUTPUT:

function myFunc() {
alert("hello John Doe");
}

How to prevent PHP echo from ending a JS string?

You should be using json_encode to output your values (and note you no longer need the enclosing "s):

i.value=<?php echo json_encode($_POST['username']); ?>;

This will ensure that quotes within the string are escaped and the entire value is treated by JavaScript as a string. For your example data, this will produce

"\";f();"


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