About a year and a half ago, I was on the hunt for my first “real” job. I knew that I wanted to be a “web developer” (whatever that entails) but I had no idea where to begin. I knew just a smidge of PHP. I was developing websites in Classic ASP at my current internship, but I knew that was an antiquidated technology which was unlikely to help me in the modern job market. As I had recently begun stomping around Hacker News, I noticed that they had a “jobs” section in their header. So I looked into things, saw that a few companies were hiring, and sent a few e-mails to companies that looked nice.
The developer who did my screen was pretty courteous and eased me into things a bit by talking about my background and experience. I sheepishly admitted that I had studied philosophy in college, not computer science, and he put my concerns at ease by telling me that their founder had never finished college. That made me feel better about things, since part of the reason I love technology so much is that it is so meritocratic.
So, without further ado, we began to investigate a coding problem.
INTERVIEWER: You’re familiar with jQuery, right?
INTERVIEWER: Great. So, you’re familiar with something like this, right? Let’s say you have a textbox and you want to make a call to the server to get some data every time the user does some typing, if you wanted to make autocomplete suggestions, for example… (begins typing into a shared/remote codepad)
ME: Oh yes, I see. When the user presses down a key on the element, we will make a call.
INTERVIEWER: So, you may be able to guess, that there is a problem with this code. It is very inefficient. If you type a string with 30 characters into the text box, the server gets called 30 times. Not good, we are having all kinds of issues with scalability so we can’t afford to be writing code like this.
Called Server 0 times…
ME: I see.
What Really Happened
ME: I think I would use… Um…
INTERVIEWER: Well, do you know what a closure is?
ME: Yeah! Closures. I’ve heard of those.
INTERVIEWER: What about
window.setTimeout ? Do you know about that?
INTERVIEWER: Kind of…
ME: I think I would… typing awkwardly and struggling for 30 seconds I guess I’m not sure.
INTERVIEWER: I appreciate your time but perhaps this isn’t a good fit.
What Should Have Happened
ME: Hm, that’s an interesting problem. So, if we use
window.setTimeout we can delay the call for 200 milliseconds.
ME: But that’s not going to help us in the case where the user is typing fast, or even just normal speed. So we need a way to interrupt the timeout if the user keeps typing.
ME: So, I know that when you call
window.setTimeout, you get back an ID that uniquely references the timeout. And you can use it to cancel the timeout if need be! So we should just store the timeout ID in the
keypress function closure, and if the user triggers a keypress event again before the timeout function triggers, we’ll just cancel it and set a new one!
(EDIT: Some commenters have pointed out that due to the fact that
this in jQuery callbacks refers to the DOM node in question, not the function closure, the ID is actually being stored as a property of the DOM node. They are correct.)
INTERVIEWER: Sounds great! What would that look like in code?
ME: It’d look a little something like this…
ME: I try.
Called Server 0 times…
INTERVIEWER: Now on to the next question…
I bombed this interview but I learned something from it. I know I could go in more confident and capable today. It just goes to show you that not every setback in life has to be a bad thing. Someday in the future I would like to work with Y Combinator or a Y Combinator-based startup, largely because I think there’s so much opportunity for learning and growth.
Thanks for reading and I’ll catch you next week,
EDIT: Some commenters have pointed out my misuse of
clearInterval as opposed to
clearTimeout. It turns out that this (mostly) works to clear timeouts, but is clearly not correct (it’s meant to be used with
window.setInterval). I have fixed this now.