PerformanceJS

a blog by Boris Cherny

Options in TypeScript

If you wrote in Scala or Haskell before you tried TypeScript, you may have found yourself wondering: Where are the Options at?

For those not familiar, here is an excellent introduction to Scala’s Option type. At a high level, Option is an abstraction over null that gives useful semantics around running functions over possibly-null values. It implements a monad, a functor, and some other structures, but that’s not important for this post.

Read more...

The Best Frontend JavaScript Interview Questions (written by a Frontend Engineer)

I was at a Free Code Camp meetup in San Francisco a few days ago (for those not familiar, Free Code Camp is a group of people who get together to learn JavaScript and web development), and someone getting ready for frontend dev job interviews asked for JavaScript questions to practice. After a bit of Googling, I couldn’t find any lists I could point her to and say “if you can do these, you can land a job”. Some came pretty close, some were silly, but all were either incomplete or asked questions that people don’t actually ask in real life.

So, based on my experiences on both sides of the interview table, here goes. These are a sampling of questions I’ve asked and been asked when hiring frontend engineers. Keep in mind that some places (like Google) focus more on designing efficient algorithms, so if you want to work there you should practice past CodeJam problems in addition to the stuff below. If you have a question that belongs in one of these lists (or I’ve made a mistake somewhere), shoot me an email.

Read more...

Introducing: Lazy Arrays in JavaScript

Today I’m introducing lazy-arr, which brings lazy arrays to JavaScript.

What’s a lazy array and why is it useful?

Flashback to your job interview for your first software engineering job: let’s write a Fibonacci function. We define the base cases of 0 and 1, then recurse to generate the rest:

Read more...

Automatically Generating Base64 Inline Images With SASS

Base64 encoding has been around for years, and when applied to images (among other data) in the form of Data URI’s, is a crucial tool in the performance geek’s arsenal.

Why Base64?

While base64 encoding increases the byte size of encoded content by around 1/3[1], it has the potential to dramatically cut down on HTTP requests and latency per resource. Since many browsers allow only a few connections per host (iOS allows 4-6, IE8/9 allows 6, and IE6/7 allows just 2, as per the HTTP 1.1 Spec), inline images are often a good alternative to many small external images, which would be forced to be fetched in sequence rather than pipelined. For relatively small media inlined in CSS, another benefit comes in the form of no more flash of unstyled content: inline images will load at the same time as the containing CSS file.

Read more...