JavaScript lets you pick between mutable and immutable styles, and the choice has real performance consequences once a JIT compiler gets involved. Immutable structures simplify reasoning, stay thread-safe across async boundaries and Web Workers, and cache cleanly for memoization. Mutable arrays and objects win on in-place updates — fewer allocations, lower memory pressure.
The full post digs into how V8-style JITs treat each style: why frequent property-type changes confuse type feedback, how a consistent shape lets the JIT apply constant folding and dead-code elimination more aggressively, and when reaching for Object.freeze or Immutable.js pays off versus when mutation is the right call.
Originally published at andreasbergstrom.dev — read the full post there.
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