TypeScript Partial and Required utility types

Partial<T> constructs a type where all properties are optional. Required<T> constructs a type where all properties are required or non-optional.

Partial:

type Cart = {
    items: Item[];
    total: number;
    startedAt: Date;
}

const updateCart = (cart: Cart, newFields: Partial<Cart>) => {
    return { ...cart, ...newFields };
}

Required:

type ProfileProps = {
    firstName?: string;
    lastName?: string;
    iconSrc?: string;
}

const Profile = ({ ... }: ProfileProps) => {
    if (!firstName || !lastName || !iconSrc) {
        return <FallbackProfile ... />
    }
}

const FullProfile = ({ ... }: Required<ProfileProps>) => {
    // Can now safely assume firstName, lastName, iconSrc are not undefined
    return (
        ...
    );
}

See Partial

See Required