What role does the empty object type {} play in typescript?

In the @types/React package of the DefinitelyTyped library, I came across this definition:

interface FunctionComponent<P = {}> {
        (props: PropsWithChildren<P>, context?: any): ReactElement | null;
        propTypes?: WeakValidationMap<P>;
        contextTypes?: ValidationMap<any>;
        defaultProps?: Partial<P>;
        displayName?: string;
    }

I learned that the default type for P is {}, known as the Empty Object type which describes an object with no properties. Does anyone know why it's commonly used as a default type for most generic functions?

typescript

Answer №1

Why is it commonly chosen as the default type for a majority of generic functions?

The reason it prevails as the default type in many React scenarios is because, if specific props are not specified, it is assumed that no props are desired. In such cases, even though your component may not have any properties defined, it will still receive an empty props object with no properties.

Answer №2

Prior to TypeScript 3.5, any type that couldn't be inferred would default to {}. Now, it defaults to unknown. This explains why older code often uses {} rather than unknown.

It's important to note the distinction between the two: {} cannot be null, whereas unknown can.

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