docs Update 03-typescript.md

[rob-balfre]

Fix TS error: Cannot invoke an object which is possibly 'undefined'.

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• This message body should clearly illustrate what problems it solves.
• Ideally, include a test that fails without this PR but passes with it.

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• Run the tests with pnpm test and lint the project with pnpm lint

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Latest commit: 0647418

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[Rich-Harris]

preview: https://svelte-dev-git-preview-svelte-14382-svelte.vercel.app/

this is an automated message

[github-actions]

Playground

pnpm add https://pkg.pr.new/svelte@14382

[dummdidumm]

thanks - but shouldn't it be adjusted for the previous code snippet, too?

[Rich-Harris]

good catch, i adjusted it. thanks!