mobxjs/mobx · warning

${msg}

Error message

${msg}

What it means

useDeprecated is a helper that warns once per unique message via console.warn when a deprecated mobx-react-lite API is called. It is not an exception — the message text passed in describes which API is deprecated and what to use instead, and the warning is deduplicated so it appears only the first time.

Solutions

1. Follow the message: replace the deprecated call with the suggested modern API (usually observer() or useLocalObservable)
2. Replace useObserver(fn) with wrapping the component in observer()
3. Remove stale options arguments to observer() and hoist dependent observables with useLocalObservable
4. Suppress only temporarily by filtering console.warn, but prefer migrating

Example fix

// before
function Comp(props) { return useObserver(() => <div>{props.name}</div>) }
// after
const Comp = observer(({ name }) => <div>{name}</div>)

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When it happens

Trigger: Calling deprecated mobx-react-lite exports such as useObserver() or observer(..., options) forms that have been superseded (e.g. by observer() without options or useLocalObservable), in a version where useDeprecated is wired to that export.

Common situations: Upgrading mobx-react-lite after 6.x where useObserver was replaced by direct observer()/React.mergeRenderless usage; copy-pasting old tutorial code; e2e logs showing one-time deprecation warnings.

Understand the failure class

Background: "is deprecated and will be removed" — deprecation warnings for old API names, keywords, and options, and how to migrate before the removal release — this error's family across 29 libraries.

Related errors

• [mobx] (error in reaction ' ' suppressed, fix error of…
• [mobx-react] It seems that a re-rendering of a React…
• [mobx-react-lite] `render` property of ForwardRef was not a…
• mobx-react-lite requires mobx at least version 7 to be…
• mobx-react-lite requires React 18 or later

AI-assisted analysis of mobxjs/mobx@01211a698b (2026-08-28). Data as JSON: /api/errors/98ebc36c25bc25e2. Report an issue: GitHub.

Appendix: source

Thrown at packages/mobx-react-lite/src/utils/utils.ts:6

const deprecatedMessages: string[] = []

export function useDeprecated(msg: string) {
    if (!deprecatedMessages.includes(msg)) {
        deprecatedMessages.push(msg)
        console.warn(msg)
    }
}

View on GitHub (pinned to 01211a698b)