zhangaz1/typescript-utilities-cheatsheet

a list of typescript helper libraries

typescript-utilities-guide

a list of typescript helper libraries. advanced guides in typescript-cheatsheets will assume knowledge of these and refer people here.

There is a stage in every TypeScript journey where you struggle getting the types you want and eventually find a lifesaver blogpost like TypeScript Types You Should Know About. This cheatsheet accumulates them.

Utility Types

Be familiar with the Utility Types that ship with TS. On top of that, here are handy Utility Types often used by TS practitioners, with explanation on what they do and how they can help. We will assume knowledge of mapped types and conditional types like Exclude<T, U> and ReturnType<T> but try to build progressively upon them.

Note: If you are new to conditional types, I highly recommend DJSheldrick's blogpost and talk on Conditional Types in TypeScript

Optionalize<T extends K, K>: Remove from T the keys that are in common with K

/**
 * Remove from T the keys that are in common with K
 */
type Optionalize<T extends K, K> = Omit<T, keyof K>;

An example usage is in our HOC section below.

Nullable<T> or Maybe<T>: Make a Type into a Maybe Type

/**
 * Make a Type into a Maybe Type
 */
type Nullable<T> = T | null
type Maybe<T> = T | undefined

Your choice of null or undefined depends on your approach toward missing values. Some folks feel strongly one way or the other.

Dictionary<T>: Dictionary of string, value pairs

/**
 * Dictionary of string, value pairs
 */
type Dictionary<T> = { [key: string]: T }

[key: string] is a very handy trick in general. You can also modify dictionary fields with Readonly or make them optional or Omit them, etc.

There also exist helper type libraries:

• utility-types
• type-zoo
• typesafe-actions
• type-fest
• tsdef
• rex-tils
• ts-toolbelt (Reddit)
• tiny-types

seriously, check some of these out, they represent a ton of accumulated typescript experience.

Type Testing

• https://github.com/SamVerschueren/tsd: Check TypeScript type definitions
• https://github.com/aikoven/typings-tester#readme
• https://github.com/ikatyang/dts-jest
• https://github.com/SamVerschueren/tsd
• https://github.com/azz/jest-runner-tsc
• https://github.com/microsoft/dtslint (Intro to dtslint)

TypeScript Plugins

You can write plugins to modify typescript syntax itself. this is ADVANCED and not exactly recommended but here are some examples if you need them:

• https://github.com/rimeto/ts-optchain/

Misc

• https://github.com/urish/typewiz Automatically discover and add missing types in your TypeScript code
• https://github.com/microsoft/rushstack/tree/master/apps/api-extractor

API Extractor provides an integrated, professional-quality solution for all these problems. It is invoked at build time by your toolchain and leverages the TypeScript compiler engine to:

• Detect a project's exported API surface
• Capture the contracts in a concise report designed to facilitate review
• Warn about common mistakes (e.g. missing exports, inconsistent visibility, etc.)
• Generate *.d.ts rollups with trimming according to release type
• Output API documentation in a portable format that's easy to integrate with your content pipeline

Codegen from TypeScript

• https://github.com/yousefed/typescript-json-schema
• https://github.com/apollographql/apollo-tooling/tree/master/packages/apollo-codegen-typescript

Data Structures

https://github.com/basarat/typescript-collections