' after the timer value, then proceed to construct a JS expression that will be evaluated before the call to setTimer ... Hint: '99'+moo() will evaluate nicely. Don't forgot the "open" the ' again.

I can't figure how to close the quote after the '99 ? I realise that specifying ' on URL gets encoded to %27 but not sure how to turn that into the closing ' for startTime('99'); .....

Help!

Can you elaborate on this? I tried that and got "unexpected identifier" as a console error. Not sure how it works.

The point is to break out of the startTimer() function call, e.g.:

    startTimer('');foo();//');

The remaining '); can be commented out in order to not create any syntax errors.

SPOILER ALERT

I used this: 1'* alert()* '

(without the spaces needed for markdown here)

Could you explain why the * works in there?

JS does automatic type conversion in this case, so it's syntactically correct to multiply a string with a number (or function result). We're just interested in the side-effects of alert(), so it doesn't really matter what kind of expression we use it in, as long as it parses correctly and causes alert() to be executed (evaluated).

Nice!

still not able to get :-(

Use the text input instead of the url.

You could use %2b instead of + on the URL and it'll work, or just * as mentioned above.

' + alert() + '

worked for me.

can't solve it either :-/

In the text input I put:

3') + alert('