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How to fix TypeScript error: expression of type can't be used to index type All In One

发布时间 2023-09-26 15:06:33作者: xgqfrms

How to fix TypeScript error: expression of type can't be used to index type All In One

errors

Element implicitly has an 'any' type, because expression of type '' can't be used to index type ''.

image

https://stackoverflow.com/questions/77177225/how-to-access-the-string-index-of-a-typescript-type-that-mixes-known-and-unknown/77177386#77177386

https://stackoverflow.com/questions/63430129/how-to-mix-index-signature-with-known-properties/63430341#63430341

solutions

  1. type guards
// const txt = foo["txt"]

let txt;
// ✅
if('txt' in foo) {
   txt = foo["txt"]
}

TypeScript Playground

  1. keyof
// const txt = foo["txt"]

// ✅
const txt = foo["txt" as keyof FooBar]
  1. keyof + typeof
// const txt = foo["txt"]

// ✅
type KT = keyof typeof foo;
const txt = foo["txt" as KT]

demos

TypeScript Playground

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Narrowing

https://www.typescriptlang.org/docs/handbook/2/narrowing.html#typeof-type-guards
https://www.typescriptlang.org/docs/handbook/2/narrowing.html#instanceof-narrowing
https://www.typescriptlang.org/docs/handbook/2/narrowing.html#control-flow-analysis
https://www.typescriptlang.org/docs/handbook/2/narrowing.html#using-type-predicates

https://www.typescriptlang.org/docs/handbook/2/classes.html#this-based-type-guards
https://www.typescriptlang.org/docs/handbook/2/conditional-types.html#conditional-type-constraints

cheatsheets

image

https://www.typescriptlang.org/cheatsheets

refs

https://bobbyhadz.com/blog/typescript-element-implicitly-has-any-type-expression

https://www.totaltypescript.com/concepts/type-string-cannot-be-used-to-index-type

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