Hey everybody, I'm Pete. So, who is exited for some big O-notation in the morning? Alright, alright, so we gonna get to that. but before we do i'm just gonna say I'm Pete. I work at Facebook on the Instagram team and I'm a contribute to a library called react which you may have heard is the one that puts the angle brackets in your javascript .. but, I'm not gonna really talk to much of that React and why it is so awesome because that's not the interesting part what I wanna talk about the ideas behind React and React is a reference implementation of those ideas. So. This isn't a turial and I give a focus on ideas and not implementations. So. I'm gonna talk about the ideas behind react Some ideas behind other systems how they're a different kind a what a different tradeoffs are in there are different tradeoffs between them and hopefully you take some of the ideas and bring them to your favourite system or you maybe you think that react is cool and you can tribute to it. Lets talk about what makes user interfaces difficult to build. Has anyone build an user interface before? Alright, OK. I figured it. Was it really easy? Yeah, testing it was super-easy, maintainng quality was probably a joke, right. It's just a kind a .. always works He said sarcastically But you get this a lot This doesnt feel right So, you know - even if you use all the test driven development that you can throw at it you still have to have a human look at this this doesnt look right and this doesnt fell right and when I click this button and I click this button and I click this button ... it breaks There's a lot of things that come in to this They are human verifiedy but UIs are also deceptely complex