TypeScript Articles by Matt Pocock

Learn the differences between React.ReactNode and JSX.Element in TypeScript when working with React.

Since I first got into advanced TypeScript, I've been in love with a particular pattern. It formed the basis for one of my first-ever TypeScript tips, and it's been extraordinarily useful to me ever since. I call it the IIMT (rhymes with 'limped'): the Immediately Indexed Mapped Type.

There are three rules to keep in mind when deciding where to put types in your application code.

Discover the power of ComponentProps in React and TypeScript. Learn how to extract and utilize props from native HTML elements, existing components, and elements with associated refs. Enhance your development workflow with this essential type helper.

Testing types is a crucial aspect of developing libraries in TypeScript. In this article, we explore three different ways to test your types: using the vitest test runner, rolling your own solution with type helpers, and leveraging the tsd library.

The TypeScript 5.1 beta is out - here's everything you need to know.

Testing code doesn't need to be typed so strictly, and sometimes tests need to pass the wrong type. I made a library called shoehorn that eases the pain of working with tests in TypeScript by providing a first-class way to pass the wrong type to a function.

The article discusses why TypeScript does not throw an error when a function that is assigned to a variable doesn't match its type. It explains that a function with fewer parameters than its type can still be passed, and this behavior is not restricted to TypeScript but exists in JavaScript as well.

TypeScript 5.0 introduces const type parameters which are useful in preserving the literal types of objects passed to functions.

Exclude is a very powerful utility type that can be used in a variety of ways. In this article, I'll show you 9 ways to use it along with code examples.

As a frontend developer, your job isn't just pixel-pushing. Most of the complexity in frontend comes from handling all the various states your app can be in.

It might be loading data, waiting for a form to be filled in, or sending a telemetry event - or all three at the same time.

If you aren't handling your states properly, you're likely to come unstuck. And handling states starts with how th

Using the satisfies keyword is one of four ways to make type assignments in TypeScript. In this article we'll look at examples of when each method should be used.

Understand why TypeScript throws complicated errors by learning how to read them. Errors mirror the structure of the code being compared and can be simplified by changing the way types are assigned.

Learn how to use TypeScript generics on the type level and with functions to improve code readability, type safety, and reduce repetitive code. Use "type helpers" to create new types and generic functions to pass in and return specific types.

Use Zod to validate unknown inputs in your app, whether it's a CLI or a public API, to ensure that data entering your app is safe. Zod can also be used for 'sort of' trusted inputs, like third-party services, to ensure that the data returned is what you expect.

TypeScript's template literal syntax allows developers to manipulate and transform strings in a powerful way. This can be extended using unions, infer, and recursion to handle more complex tasks.

Donny (kdy1 on GitHub) is rewriting TypeScript in Rust hoping to speed up tsc which is slow due to its TypeScript base. In this interview, he explains some of the financial and technical challenges they face with this open-source project.

Let's imagine you're creating a function which sums up an array of objects. Here's one, taken from the Excalidraw codebase:

const sum = <T>(array: readonly T[], mapper: (item: T) => number): number => array.reduce((acc, item) => acc + mapper(item), 0) 

Let's look at the type definition. This function takes in:

• An array of something: readonly T[]
• A mapper function: `(item