Typescript array typing

Hey I was wondering why typescript doesn't indicate that the name here is possibly undefined when the arr is empty?

type T = { name: string }[];

const arr: T = [];

const name = arr[0].name; // no ts error but it throws Cannot read properties of undefined

type T = { name: string }[];

const arr: T = [];

const name = arr[0].name; // no ts error but it throws Cannot read properties of undefined

5 Replies

cje•2y ago

depends on your tsconfig

cje•2y ago

this might help https://www.typescriptlang.org/tsconfig#noUncheckedIndexedAccess

TSConfig Reference - Docs on every TSConfig option

From allowJs to useDefineForClassFields the TSConfig reference includes information about all of the active compiler flags setting up a TypeScript project.

stanisław•2y ago

Thats what I thought Strange that default create next app doesnt have this option turned on Thanks

cje•2y ago

create next app has a history of not being great at ts by default

JacobMGEvans•2y ago

They are improving. Just by having TS as default, I'll take that W 😆

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Typescript array typing