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Dmitri Pisarev 🇷🇺
Dmitri Pisarev 🇷🇺

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Annoying TypeScript discriminating union gotcha

#typescript

Can you spot what's wrong with this code?

Discriminating union gone wrong

https://www.typescriptlang.org/play?ts=4.2.3#code/C4TwDgpgBACgTgezAZygXigbwFBT1AS2QEE44BDEALigDNyAbZCAGl31oDsaAKAN0YBXCDWTA4BTgHMAlOgB8UPggIATbAF8oAHyzs8RUhWpRxwtvjrco-ISKhiJ0gNoBdOWkXK1m7NgDGCJxiUADCCAC2YEEQnMDoNpiGZJQsVho08EjIHoo4loHB8f6MDABG5P4A1gk8uXqWlgS0NsnGcvmNXVw8zgDk5MiqtKp97vqNWhBM0J1dlj19AIwATADMfTITlhoTuxpAA

Top comments (2)

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sevaru profile image
sevaru •

TLTR It would work if you write like this

const Component = (props: Props) => { const callback = () => { if (props.isArray) { props.fn(['asdfd']) } else { props.fn('123') } } }
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dimaip profile image
Dmitri Pisarev 🇷🇺 •

Yup, exactly! During restructuring TypeScript looses relation between object members.