[austincheney]

No, its a common misunderstanding of search and tree models. The OS is faster, by a tiny bit, at traversing the file system than my JavaScript application. It is only search that is slower, and dramatically so. I don't have visibility of the OS code so I cannot be certain why that is. I speculate its because the OS is doing too much.

With the DOM querySelectors are dramatically slower than using static methods with arbitrary strings as arguments. This is likely because a query string must be parsed against each child node to determine if the child node is a match to the supplied query. Likewise, modern OSs use ancient conventions to search the file system, such as wildcards, along with more modern advanced search syntax. These are rules that must be parsed against each child artifact from a tree segment. My application deliberately doesn't do that.

To compound matters Windows, don't know about OSX, caches search results so that subsequent searches are a little less slow, which incurs a greater performance penalty on first search. My application doesn't do that either. Each search triggers tree traversal, so its always as fast reading from the file system.

Mentioning any of this during a job interview makes for intriguing conversation with the interviewer. I do detect genuine interest and curiosity from the interviewer. At the same time they know their team will fight to the death at many mention of alternatives to querySelectors and/or JSX, so you have just effectively terminated the interview. Anything there after is purely for the interviewer's personal interests.

[greggman3]

No app I've ever written needs querySelector to be fast. I'm not saying I can't imagine such an app. But, I would never reach for some optimized but very uncommon solution unless the app really needed it.