php - Why won't this code work?

Question

Can anyone tell me why this code won't work?

<?php $err=1; ?>

<img src="334234234234234.gif" onError="<?php $err=0; ?>" />

<?php echo "<br />" . $err; ?>

Even when the image exists, the onerror is still executed. Why?

Answer 1

HTML cannot set PHP variables. Those can only be set while on the server. The onError method of the IMG tag has no access to PHP variables.

The page life-cycle:

1. (SERVER) The server builds your page (handling variables, etc)
2. (SERVER -> CLIENT) The server sends out the page to the client computer
3. (CLIENT) The html is loaded, javascript is ran, and any errors are raised.

Note, you're attempting to combine item 3 with item 1, which cannot be done semantically.

The only way to do what you're attempting would be to attach a javascript method to that event, and communicate to the server when and if the onError method is ran. But this is likely going to be a bit more complicated than you're use to.