JavaScript Performance Gotchas: Avoid scaling issues through under-the-hood knowledge

JavaScript engines have gotten remarkably efficient, but a handful of common idioms still leak performance — and the cost compounds fast on the server, where a minor allocation in a hot path becomes a scaling cliff. This post walks through five of those gotchas, side-by-side, with a clear verdict for each.

It covers array.push vs. the spread operator, for / forEach vs. for...in on arrays, +-concatenation vs. Array.prototype.join for building large strings, the cost of global vs. local variable lookups, and caching deeply nested property accesses. Part 2 of the series is 5 More JavaScript Performance Gotchas.

Originally published at andreasbergstrom.dev — read the full post there.