Typescript Trick

generic types optional

To make a generic type optional, you have to assign the void as the default value.

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const fetchData = <T = void>(url: string): T => {
    const res: T = fetch(url);
    return res;
};

https://garbagevalue.com/blog/optional-generic-typescript#quick-solutions-make-generic-type-optional

string[ ] & [ string, …string[ ] ]

The main difference is that type [string, ...string[]] at least have one element. [] will alert error. string[] could be empty. [] is ok.