Building dynamic arrays in JS is often messy. It goes like this: you have a default array, and you need some items to appear based on a condition. So you add an if (condition) array.push(item). Then you need to shuffle things around and bring in an unshift or two, and maybe even a splice. Soon, your array building code is a crazy mess of ifs with no way to tell what can be in the final array, and in which order. Something like this (yes, I'm building a CLI lint runner):
