typescript-toolbelt

Helpers & utility types for TypeScript projects.

Usage

To put type helpers into the global scope:

/// <reference types="typescript-toolbelt/global" />

...or add to your tsconfig's "files" or "include" array:

"files": [
    "node_modules/typescript-toolbelt/global.d.ts"
]

To expose type helpers as a global TT namespace, reference typescript-toolbelt/namespace:

/// <reference types="typescript-toolbelt/namespace" />

...or put it in your tsconfig as shown above.

A few helpers require a runtime value. This will be an identity or no-op function. Thankfully, these should be removed or inlined by a code minifier and/or the JS VM. These must be imported, because it would be messy to attach them to the global object.

Fortunately, if you're using a supported editor, you can reference them in code and the language service will offer to write the import statement for you.

import { narrowLiterals } from 'typescript-toolbelt';
 
const foo = narrowLiterals(['a', 'b', 'c']);

React-specific helpers should be imported from typescript-toolbelt/react. These can't be loaded by default because they have a peer dependency on @types/react.

Docs

Until I get around to generating a website from the documentation, use tab-complete in your editor to see the list of helpers and flip through their documentation. Or read the source.

Things already bundled in TypeScript

TypeScript already includes a bunch of type declarations you might not be aware of. Here's an incomplete list:

ArrayLike<T> // Minimal Array interface, without all the obscure methods and Symbols.
 
Partial<T> // T, except all properties are optional
Required<T> // T, except none of the properties are optional
 
Record<K, T> // object-based map from K to T
 
Readonly<T> // T, except all properties are readonly
ReadonlyArray<T> // Readonly array.  Type system will forbid assignment to items and accessing methods that mutate, like `push()`
ReadonlyMap<K, V> // Readonly ECMAScript Map
ReadonlySet<V> // Readonly ECMAScript Set
 
Extract<T, U> // filter a union type T to only the types that extend U
Exclude<T, U> // opposite of Extract; filter union T to only the types that *do not* extend U
 
NonNullable<T> // Remove `null` and `undefined` from a union type.
 
ReturnType<F> // Extract the return type of an invokable type (function)
InstanceType<C> // Extract the instance type of a `new`-able type (constructor)
 
Pick<T, K> // Grab only properties K of interface T.  Useful with `Extract`, `Exclude`, and `keyof`

---

TODO

• add DeepReadonly, DeepMutable, DeepPartial, DeepRequired, DeepNonNullable, DeepNullable (any others?)