Creating a javascript alert with php that has a php variable inside?

Question

I'm making a form that is supposed to create a javascript alert when some fields aren't filled out or filled out properly. I want to be able to take the error messages I've put in a php variable and display them in the javascript alert window.

The following code does not work:

function died($error) {
 echo '<script type="text/javascript"> alert('.$error.')</script>';
 die();
}

How can I add the string contained in $error between the two "script" strings so it will output properly as a javascript alert?

Thank you!

• Eddie: do you want to append the $string and $error variables?
• David Corbin: Why not use javascript to detect if all the forms are filled in?
• MarvinLazer: Sorry, I screwed up and added an old version of the code I was using to figure out what was wrong. The $string variable is completely unnecessary. I took it out. Thank you!
• Eddie: You just can do a client checking if you just want to 'alert' the error.. but then again the best way to validate is in the server side.

Answer 1

You only forgot quotations that are required for the JavaScript alert.

If you passed 'hello' to the function, your current code would create alert as:

alert(hello)

instead of doing:

alert("hello")

Therefore, change your code to the following (json_encode() the string and create a javascript variable out of it):

function died(string $message) {
 if ('' === trim($message)) {
 $message = 'died.';
 }
?>
 <script type="text/javascript">
 var message = <?php echo json_encode($message); ?>;
 alert(message);
 </script>
<?php
 die();
}

and you can use your function:

died('error on whatever');

• MarvinLazer: Thanks! It works, although I don't really understand why. What if I wanted to add other text in the alert that would be concatenated with the variable? Would I have to do something like this? echo '<script>alert('.'Here is some other text!\\n"'.$error.'");</script>'
• user1978142: as @frankgorman clearly stated, what happens is that, after you concatenated, you missed the quotes inside rendering the error on javascript. If you want to add, just concatenate another string on $error. Example: $error = "Another Line \n" . $error
• Eon: You know you are very new to a language when you look for ways to alert/log variables :) (happens that I came to search for this answer too)
• Scarl: This displays nothing. As in it does not display the php variable's value for some reason
• Crickets: Your answer did not work for me, but this did: echo '<script>alert("' . $str . '");</script>'; -source

Answer 2

Display variable php in alert javascript

 <?php 
 function died($error) { ?>
 <script>alert("<?php echo $error; ?>")</script>
 <?php die(); 
 } ?>

Answer 3

You can use function follow this:

function died($error) {
 echo '<script> alert("'.$error.'")</script>';
 die();
}

Answer 4

<?php
 echo "<script type='text/javascript'>alert('{$_SESSION["success"]}');</script>";
 unset($_SESSION["success"]);
?>

Use this code it would work correctly

• Giovanni Esposito: Ciao, try to add a small explanation. Code-only answer discourages.