Clamp every console.log argument before it crosses the Capacitor JS↔native bridge

#1—Context

We saw 1,900 OutOfMemoryError crashes in a 7-day window from a single Crashlytics signature. One user hit the same crash 13 times in a row. Every crash tried to allocate the exact same 266 MB block. Only on TECNO, Vivo, and Infinix — the low-RAM Android devices a large share of our users actually carry. Two days of guessing — images, leaks, IndexedDB, Dexie — all wrong.

#2—Options considered

A
Leave it (won't-fix) — 1,900 crashes/week on the devices our actual users carry. Not an option.
B
Strip console.log at build only (Terser) — Already in place — and the Terser config had quietly regressed, which also stripped our Crashlytics breadcrumbs. One layer is not enough; build config drift is silent.
C
Runtime clamp at the bridge — Wrap console.* and truncate any argument over 8 KB before it crosses the bridge. Survives Terser regressions and works in dev builds too.
D
Abandon Capacitor — Too expensive for a bug this localized. Re-evaluate only if the bridge keeps producing structural failures.

#3—Decision

Defense in depth across four layers: (1) Terser strips console.* calls in production builds. (2) A runtime guard wraps console.* and clamps any single argument to 8 KB before it can be marshalled across the JS-to-native bridge. (3) An agent safety rule rejects new code that logs raw response/record/err objects. (4) Fixed a separate Terser config issue that had been stripping Crashlytics breadcrumbs in prod.

#4—Trade-offs

Engineers lose the ability to console.log a raw 1 MB object. They now have to log shape — `console.log("saved", { id, status })` instead of `console.log(response)`. Minor DX cost; we measured zero developer-velocity impact in the week after rollout.

#5—Revisit trigger

If Capacitor patches its String.format usage on the Android bridge — or if we move off Capacitor entirely — the runtime clamp can be relaxed back to a simple level guard. Build-time stripping and the agent rule stay regardless.

#6—Takeaways

01
Read the SDK source. Third-party libraries feel like black boxes until you open them — the production issue costing you thousands of crashes may sit in 40 lines of code nobody on the team has ever read.
02
console.log(object) in a mobile WebView is structurally dangerous, not stylistic. Prefer console.log('saved', { id, status }); avoid console.log(response) / console.log(record) / console.log(err).
03
Defense in depth wins. Any one layer (build-strip, runtime guard, agent rule, breadcrumbs) can regress. All of them together stay resilient.
04
On low-RAM Android (TECNO/Vivo/Infinix) the WebView heap tops out around ~192 MB. Treat that as a hard ceiling for any data that crosses the JS-native bridge.

#7—Full write-up

What I blamed first (and got wrong)

Two days, three wrong hypotheses:

Image handling — overzealous bitmap caching.
Memory leaks — long-lived references in a Dexie subscriber.
IndexedDB / Dexie — too-large records pulled into memory.

Every assumption was wrong. The crashes all tried to allocate the same 266 MB block, and the only signal connecting them was the device class — TECNO, Vivo, Infinix. Nothing in our JS code path touched that much memory.

What cracked it open

I stopped guessing and read the Capacitor source. The bridge runs Java's String.format on every console.log message before any log-level or production guard kicks in. So when JS does:

console.log(response);

…and response is a large Dexie object with embedded base64 audio, Java tries to materialize the entire thing across the JS↔native bridge. On low-RAM devices the WebView heap caps around 192 MB. The 266 MB allocation goes through String.format, OOMs, and the app dies instantly.

The whole story was sitting in ~40 lines of Java that nobody on the team had ever opened.

The fix

Four layers, intentionally:

// Runtime guard installed at app entry, before any feature code runs.
const MAX_ARG_BYTES = 8 * 1024;
const truncate = (arg: unknown): unknown => {
  if (typeof arg !== "string") {
    try {
      arg = JSON.stringify(arg);
    } catch {
      return "[unserializable]";
    }
  }
  const s = arg as string;
  if (s.length <= MAX_ARG_BYTES) return s;
  return `${s.slice(0, MAX_ARG_BYTES)} … TRUNCATED ${s.length - MAX_ARG_BYTES} chars`;
};

for (const level of ["log", "info", "warn", "error", "debug"] as const) {
  const original = console[level].bind(console);
  console[level] = (...args: unknown[]) => original(...args.map(truncate));
}

Chat with Shoaib

Chat with Shoaib

Clamp every console.log argument before it crosses the Capacitor JS↔native bridge

What I blamed first (and got wrong)

What cracked it open

The fix

Result

If you ship Capacitor, Cordova, or any JS-to-native shell