mobxjs/mobx · error

[MobX] ${e}

Error message

[MobX] ${e}

What it means

MobX's internal die() raises all developer-facing invariant violations. In __DEV__ builds it resolves a message key or template from the niceErrors table (optionally formatting it with args) and throws `[MobX] <message>`. It is the single funnel for every 'you used MobX wrong' assertion, so the specific message after [MobX] tells you which invariant was violated.

Source

Thrown at packages/mobx/src/errors.ts:97

    },
    43(annotationType, name, kind) {
        return (
            `Cannot apply '${annotationType}' to '${name}' (kind: ${kind}):` +
            `\n'${annotationType}' can only be used on properties with a function value.`
        )
    },
    44(annotationType) {
        return `'${annotationType}' can only be used with 'makeObservable'`
    }
} as const

const errors: typeof niceErrors = __DEV__ ? niceErrors : ({} as any)

export function die(error: string | keyof typeof errors, ...args: any[]): never {
    if (__DEV__) {
        let e: any = typeof error === "string" ? error : errors[error]
        if (typeof e === "function") e = e.apply(null, args as any)
        throw new Error(`[MobX] ${e}`)
    }
    throw new Error(
        `[MobX] minified error nr: ${error}${
            args.length ? " " + args.map(String).join(",") : ""
        }. See mobx.js.org/errors`
    )
}

View on GitHub (pinned to 01211a698b)

Solutions

1. Read the text after the `[MobX]` prefix — it is the specific violation — and fix the offending call
2. Look up the error text at mobx.js.org/errors for the detailed explanation
3. Ensure decorator/annotation targets match their types (observable on properties, action on methods, etc.)
4. Pass valid arguments: check the API signature for autorun/reaction/computed/extendObservable

Example fix

// before
computed(() => this.value * 2) // called as method, invalid usage
// after
get doubled() { return this.value * 2 } // or makeObservable(this, { doubled: computed })

null

function isMobxError(e: unknown): e is Error & { message: string } {
    return e instanceof Error && e.message.startsWith('[MobX] ')
}

try {
    autorun(() => { /* ... */ })
} catch (e) {
    if (e instanceof Error && e.message.startsWith('[MobX] ')) {
        console.error('MobX invariant violated:', e.message.replace('[MobX] ', ''))
    } else throw e
}

When it happens

Trigger: Any MobX API invariant violation funneled through die(), e.g. calling autorun/reaction/computed with invalid arguments, misusing extendObservable, applying a decorator annotation to the wrong kind of member (assert20223DecoratorType), or passing an error code key from the errors table.

Common situations: Misconfigured decorators on non-observable class members; calling APIs with wrong arity/types; state mutations outside actions with enforceActions enabled; version-mismatched usage patterns after upgrading MobX.

Related errors

• mobx-react-lite requires mobx at least version 7 to be avail
• mobx-react requires mobx to be available
• [mobx-react] Cannot read "${admin.name}.${key}" in a reactiv
• [MobX] minified error nr: ${error}${args.length ? " " + args
• WARNING: Debug feature only. MobX will NOT recover from erro

AI-assisted analysis of mobxjs/mobx@01211a698b (2026-08-28). Data as JSON: /api/errors/0504e47147588fe9. Report an issue: GitHub.