posthog was already loaded elsewhere"

TL;DR

Fix: Recommended best practice from the maintainer: own the initialization yourself, call posthog.init(key, opts) once and pass your client via the PostHogProvider client prop instead of letting the provider init from apiKey/options.

The error

Console warning `[PostHog.js] was already loaded elsewhere. This may cause issues.` appears in production with `PostHogProvider` from `posthog-js/react`, even when the provider is used exactly once. Reported against Gatsby, Next.js, and Vite apps.

Fix

1. Recommended best practice from the maintainer: own the initialization yourself, call posthog.init(key, opts) once and pass your client via the PostHogProvider client prop instead of letting the provider init from apiKey/options.

Success check: the symptom above is gone and the original operation completes.

When to use

• You hit this exact symptom in posthog-js.
• You want the verified fix without digging through the thread.

When not to use

• A different error in posthog-js, even a similar-looking one.
• General posthog-js setup or credential questions.

Compatibility

• Posthog Js (PostHog/posthog-js)

Variant phrasings

• How to fix "posthog was already loaded elsewhere"" in posthog-js
• posthog-js: posthog was already loaded elsewhere"

Source

• https://github.com/PostHog/posthog-js/issues/723

In gh:PostHog/posthog-js#723 (https://github.com/PostHog/posthog-js/issues/723), the question was: Console warning [PostHog.js] was already loaded elsewhere. This may cause issues. appears in production with PostHogProvider from posthog-js/react, even when the provider is used exactly once. The verified resolution: Maintainer rafaeelaudibert traced much of it to React StrictMode's double-render in dev and proposed PR #1676 to detect StrictMode and skip the warning. Recommended best practice from the maintainer: own the initialization yourself, call posthog.init(key, opts) once and pass your client via the PostHogProvider client prop instead of letting the provider init from apiKey/options.