Wednesday, March 30, 2016

Dependency Cost

Over the weekend I was alerted to a bug in the web application by a reader. For him, the "previous" and "next" navigation links would not work. Clicking on them put the page into endless "Grabbing Frogs" mode and never displayed another comic.

Fortunately, the issue was not difficult to correct. Since is (almost) a single-page-application, each time a new comic replaces the currently visible one I have to generate a new Pinterest button for the correct comic. Yeah, you're probably wondering, "why a Pinterest button?" I don't know. It seemed like a good idea at the time...

I'm generating the new button by calling a slightly undocumented function in the Pinterest code. I don't think they intended for it to be used on pages quite like mine. The problem arises when the function is unavailable. Maybe Pinterest is blocked. Maybe Pinterest is down. Maybe certain browsers actually download an older version of the code where that function doesn't exist. Doesn't matter why - the end result is the same. Without that function, an error occurs in my JavaScript and the new comic is never displayed. I fixed this issue and then immediately found another similar issue with my call to Emoji One's JavaScript. Fixed that too.

This got me thinking about what I'll call Dependency Cost. I didn't really think about the cost of my code being dependent on Pinterest and Emoji One behaving in a certain way. I don't control either of them, and they could change or vanish at any time - resulting in my comic readers getting shut out of my site. When you think about it, this is really an unacceptable situation. But how many situations like this are you in right now with your code? I think we're all in too many. Take the setup for example - it's built on Node using Express and over a dozen other modules all downloaded from npm at first install. What if I had to recreate the site and npm was down. Do I think npm will be around forever? Nothing lasts forever.

Just something to think about when you're building your next application. Or you can think about today's comic. That's much more fun. comic for 30 March 2016

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