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TypeScript 的关键字 infer 有什么作用

前端 TypeScript 面试题, TypeScript 的关键字 infer 有什么作用?

前端 TypeScript 面试题, TypeScript 的关键字 infer 有什么作用?

QA

Step 1

Q:: What is the purpose of the 'infer' keyword in TypeScript?

A:: The 'infer' keyword in TypeScript is used within conditional types to extract and infer the type of a particular element. It allows you to create more complex and reusable type definitions by inferring types from certain positions within other types. This is particularly useful when working with utility types and type transformations.

Step 2

Q:: Can you provide an example of how 'infer' is used?

A:: Certainly! Consider the following example:

 
 type GetReturnType<T> = T extends (...args: any[]) => infer R ? R : any;
 
 const fn = (x: number) => 'hello';
 type ReturnTypeOfFn = GetReturnType<typeof fn>; // 'ReturnTypeOfFn' will be inferred as 'string'

In this example, the 'infer R' keyword is used to infer the return type 'R' from the function type 'T'.

Step 3

Q:: What are some common use cases for the 'infer' keyword in TypeScript?

A:: The 'infer' keyword is commonly used in utility types to extract types from function signatures or tuples, enabling the creation of more flexible and reusable types. For example, it is used in utilities like ReturnType``, Parameters``, and ConstructorParameters``, which infer types from functions and constructors. It's also valuable in creating custom type utilities where dynamic type extraction is required.

Step 4

Q:: What are the limitations or challenges of using 'infer' in TypeScript?

A:: 'Infer' can only be used in conditional types, which can make its application somewhat limited. Additionally, because 'infer' relies on conditional types, the logic can become complex and difficult to read or maintain in larger codebases. Developers need to be cautious with its use to avoid over-complicating type definitions.

用途

The `'infer' keyword is important in TypeScript because it allows developers to create flexible and reusable type utilities. In a production environment, this is particularly useful when building large-scale applications where types need to be dynamically inferred or transformed. For instance, when working with third-party libraries, APIs, or complex data structures, 'infer' helps in accurately typing return values and parameters without hardcoding types. This improves code maintainability and type safety, reducing the likelihood of runtime errors.`\n

相关问题

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What are conditional types in TypeScript, and how do they work?▷

Conditional types in TypeScript are types that are based on a condition. They follow the syntax T extends U ? X : Y``, where if type 'T' extends type 'U', the type will be 'X'; otherwise, it will be 'Y'. They allow for more dynamic type logic, enabling developers to create types that adapt based on the input types.

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How does TypeScripts ReturnType utility type work?▷

The 'ReturnType' utility type in TypeScript is a predefined type that extracts the return type of a given function type. For example, given a function type Fn = () => string``, ReturnType<Fn> will be string``. It uses the 'infer' keyword internally to perform this extraction.

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What is the difference between infer and extends in TypeScript?▷

'Extends' in TypeScript is used to perform a check or constraint on a type, ensuring that one type is a subtype of another. 'Infer,' on the other hand, is used to extract and infer a type from a position within a conditional type. While 'extends' checks and constrains types, 'infer' captures and assigns them.

🦆
What are mapped types in TypeScript, and how do they relate to infer?▷

Mapped types in TypeScript allow you to create new types by transforming each property in an existing type. They are defined using a syntax similar to array or object destructuring. While 'infer' isn't directly used within mapped types, they both serve the purpose of creating dynamic and flexible types in TypeScript. Mapped types can often be combined with conditional types, where 'infer' might be used to infer types from properties.

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