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Comment by cperciva | Hacker News Reader

Show, don't tell.

Don't tell me (or pg, or anyone else) that Comet is a cool new technology which will transform the web -- show us something which you can do with it. Lots of people say "hey, I'm cool", but few of them actually are -- until you show us something which your cool new technology can do for us, you fall into the category of unsupported hype.

We were ultimately not given funding, probably because our proposal seemed to be "Look at this cool new technology that will transform the web. We're experts on it." rather than "Here is exactly what we want to make and precisely how we'll make money."

I obviously can't read pg's mind, but I strongly suspect the issue was more that you hadn't convinced him that Comet was useful rather than due to your lack of concrete business model.

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Correct me if I'm wrong but hasn't "Comet" been around for ages? - the only change is that someone has put a catchy name to it. Or is it something more than using iframes to keep a connection open to the server and stream live data over that connection?

Indeed. The same is true of ajax really.

cperciva: on the one hand, you're right -- We didn't convince YC that Comet was a useful technology. But its not a matter of showing versus telling. We showed a few prototypes (http://www.orbited.org/livehelp.html for example) and proved that we could do cool things. The Rejoinder was, "But flash can do that." and we were unprepared for that response. The point of the article is to illustrate that pure html/javascript technology apparently is given no credence in the eyes of YC, an important player in the venture industry.

I clearly think Comet is a useful technology, but then again, I lead development on an open source comet server (Orbited) and I write for www.cometdaily.com. So why doesn't someone more unbiased let me down easy. That is, explain to me why Comet is not a useful technology.

I did look at Comet when it was mentioned here a while ago and my general reaction was that it was total overkill for most applications. It's worth remembering that the so called 'Push Technology' of the 1990s (such as PointCast) was doing a straight HTTP GET at regular intervals, the only push was that the user didn't push a button for an update. Now in the noughties we're doing similar stuff in the background with XHR polling from timers.

If what you really want to do is _real time_ pushing of data to the client then you need to come up with a really compelling situation in which that's needed. The current Comet proposal seems as you say somewhere on your blog "a big hack". What it really needs is simplicity. Tell me how this is better than polling using XHR.

In fact, if you want to excite me then give me a chunk of Javascript that as the following methods:

stream_to_me( url, callback )

I call this, it returns to me immediately. It handles a background connection to url and streams data off it using standard HTTP (perhaps it's holding a connection open, perhaps it's polling, user shouldn't care and should be transparent to the remote web server).

When it's got a complete chunk of data (perhaps it's a complete piece of XML) it calls callback with the chunk.

That would be compelling to me because I could just include that little library and then get async. callbacks with data coming 'live' from my server.

The JavaScript you described exists - it's called dojox.comet, and it looks like this:

dojox.cometd.init('http://example.com/cometd'); dojox.cometd.subscribe('/channel', callback);

That's basically what you described, but with the additional concept of "channels" to make it easy to support lots of different event streams.

I wrote more about this here: http://simonwillison.net/2007/Dec/5/comet/

Nothing is really ever about technology; it's about its application. And no one is willing to pay their time/effort/etc. to a new technology unless it has seriously significant advantages. So what is the application that Comet provides that is a killer?

I think that anyone with a technical background would agree that technologies like comet are useful. But it seems like yc wanted you to differentiate comet from the other approaches.

How would you even make money off comet based widgets or even some kind of platform for making them? The problem is that no one wants to pay for development platforms or pre-built widgets. All of the best stuff in this category is free....django, YUI, jquery, rails, comet blah blah....

Framing it in terms of useful technology or not is kind of missing the point. AJAX is good enough, or at least almost all developers out there think so.

What are you planning to do? Make something for end users, or a tool kit for developers?

Either way, you've got to bring some real value to the table. Cleaner code or xy% reduced bandwidth isn't going to cut it. You have to have concrete benefits. What does this technology enable that wasn't possible before?

If you can answer that question, you're good to go. If you can't, no ammount of justification or 'developer education' will save you.

You can't manipulate the DOM from flash. This seems to be a big difference IMO.

useful to whom?

It's obvious YC likes stuff that is made for what the mass would like to use.

I'd say YC probably choose to interview you mostly because you seemed to have talent. Maybe if you had displayed more flexibility on doing maybe other things maybe YC would not have rejected you.

I agree. I'm surprised YC didn't suggest building some consumer facing app that makes use of your comet stuff. There are many application areas that could benefit from real-time capabilities.

Also, Paul has talked about how turning a luxury into a commodity is usually a good recipe for success. Most real-time applications are very expensive and use lame desktop client/server architectures. Imagine something web-based and free that does the same thing.

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