post.php Forbidden error when saving blogpost with javascript with an if-stmt

This may be something very specific. I’ve searched the internet and find tons of information regarding the ‘forbidden’ error but nothing that comes close to this very specific case where I only encounter the error the moment I write an IF-statement in my script. (inline script in a post with <script> tags.)

I suppose php blocks this statement for some reason. Can I do something as a workaround or will I be forced to move this script to a separate JS file. It’s actually a very small script of just 20 lines and that’s why I wanted to avoid a separate call for an extra file. (SEO speedwise)