Narrow typeof x === 'object' to Record<string | number | symbol, unknown> | null | unknown[]

Search Terms

typeof object narrow record

Suggestion

When narrowing a variable with typeof x === 'object', narrow to Record<string | number | symbol, unknown> | null | unknown[] instead of object | null.

Use Cases

When testing to see if something is an object, you almost always are starting out with unknown or similarly near-top level type and trying to narrow down to a lower "useful" type. When you use the typeof x === 'object' narrowing operation, currently TypeScript over narrows to the extremely constrained {} | null type. This suggestion would change that behavior to narrow down to the much wider Record<string | number | symbol, unknown> | null | unknown[], which the user can then choose to narrow more if they like, or they can choose to work with it as-is.

Examples

declare const apple: unknown
if (typeof apple !== 'object') throw new Error() // actual: object | null; desired: Record<string|number|symbol, unknown> | null | unknown[]

// uncomment this line and comment out the lines above to see desired behavior
// declare const apple: Record<string|number|symbol, unknown> | null | unknown[]

if (apple === null) throw new Error() // actual: object; desired: Record<string|number|symbol, unknown> | unknown[]
if (Array.isArray(apple)) throw new Error() // actual: object; desired: Record<string|number|symbol, unknown>
for (const key in apple) {
    // Element implicitly has an 'any' type because expression of type 'string' can't be used to index type '{}'.
    //   No index signature with a parameter of type 'string' was found on type '{}'.
    apple[key] // actual: error; desired: unknown
}

Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

Commencez par reproduire les exemples TypeScript de l’issue et comparer le narrowing réel avec le résultat demandé. Suivez ensuite le chemin de vérification des types responsable du narrowing de typeof object, puis ajoutez ou mettez à jour la couverture pour les cas montrés de null, de tableaux et d’accès indexés ; c’est terminé lorsque ces exemples sont réduits à l’union demandée sans modifier la sortie à l’exécution.