Reflected XSS in a JavaScript URL with some characters blocked

Some websites make XSS more difficult by restricting which characters you are allowed to use. This can be on the website level or by deploying a WAF that prevents your requests from ever reaching the website. In these situations, you need to experiment with other ways of calling functions which bypass these security measures. One way of doing this is to use the throw statement with an exception handler. This enables you to pass arguments to a function without using parentheses. The following code assigns the alert() function to the global exception handler and the throw statement passes the 1 to the exception handler (in this case alert). The end result is that the alert() function is called with 1 as an argument. onerror=alert;throw 1