Every time I met my friend Antony for a drink he'd say "You still working on that little bit of JavaScript?" At the time JavaScript was mostly for little bits of web interaction and not the realm of real software engineering according to conventional wisdom, let alone a way to boost profits, but this little script increased the entire site's revenue by nearly 3%, with around £32M of sales going through it annually.

When I started working on personalisation for lastminute.com the main request was for a recommendation system, "you know, like on Amazon". Fair enough. But while looking into things there was a little insight that I decided to take advantage of first. No one books a trip on their first visit to a travel site. There's research, price comparison, checking with your partner, thinking about it, and finally booking. Meantime you visit and re-visit and re-visit the same sites. So we made a little script just to show you things you'd looked at last time, to save you time. And we created an A/B testing system as well (also a little JavaScript) so we could test whether it made a difference. Sure enough it boosted bookings by a few percent compared to the control group. And within a couple of years every big travel site had done the same thing.