Let's say I define my props like this in a child component:

type TestProps = {
    testArray: Array<string>,
    number: number
}

function TestComponent(props: TestProps)
{
....
}

and this would be the parent component.

function ParentComponent() {
    return (
        <TestComponent testArray={[1, 2, 3]}/>
        <TestComponent testArray={[1, 2, 3]} number={20}/>
    );
}

For the first JSX element, I'd like to have props.number set to testArray.length. For the second JSX element, I'd like my answer to be set to 20.

I could do something like this:

type TestProps = {
    testArray: Array<string>,
    number?: number
}

function TestComponent(props: TestProps) {
    if(props.number === undefined) {
        props.number = testArray.length;
    }
}

but I don't want that. I want a more elegant solution, somehow setting this directly in TestProps. Something similar to this:

type TestProps = {
    testArray: Array<string>,
    number: number | undefined = testArray.length
}

Is it possible?

Thanks.