Type-safe, ergonomic, polymorphic optics for TypeScript

Usage no npm install needed!

<script type="module">
  import opticsTs from 'https://cdn.skypack.dev/optics-ts';




optics-ts provides type-safe, ergonomic, polymorphic optics for TypeScript:

  • Optics allow you to read or modify values from deeply nested data structures, while keeping all data immutable.
  • Ergonomic: Optics are composed with method chaining, making it easy and fun!
  • Polymorphic: When writing through the optics, you can change the data types in the nested structure.
  • Type-safe: The compiler will type check all operations you do. No any, ever.


optics-ts supports lenses, prisms, traversals, removing items from containers, and much more!

Since optics-ts v2.2.0, there are two syntaxes for defining optics: method chaining (the default) and standalone optics (experimental). See the docs for more info!

Getting started


npm install optics-ts


yarn add optics-ts

Here's a simple example demonstrating how lenses can be used to drill into a nested data structure:

import * as O from 'optics-ts'

type Book = {
  title: string
  isbn: string
  author: {
    name: string

// Create a lens that focuses on author.name
const optic = O.optic_<Book>()

// This is the input data
const input: Book = {
  title: "The Hitchhiker's Guide to the Galaxy"
  isbn: "978-0345391803",
  author: {
    name: "Douglas Adams"

// Read through the optic
// "Douglas Adams"

// Write through the optic
O.set(optic)("Arthur Dent")(input)
// {
//   title: "The Hitchhiker’s Guide to the Galaxy"
//   isbn: "978-0345391803",
//   author: {
//     name: "Arthur Dent"
//   }
// }

// Update the existing value through the optic, while also changing the data type
O.modify(optic)(str => str.length + 29)(input)
// {
//   title: "The Hitchhiker’s Guide to the Galaxy"
//   isbn: "978-0345391803",
//   author: {
//     name: 42
//   }
// }

Another example that converts all words longer than 5 characters to upper case:

import * as O from 'optics-ts/standalone'

const optic = O.optic<string>().words().when(s => s.length >= 5)

const input = 'This is a string with some shorter and some longer words'
O.modify(optic)((s) => s.toUpperCase()(input)
// "This is a STRING with some SHORTER and some LONGER WORDS"

See the documentation for a tutorial and a detailed reference of all supported optics.


Run yarn to install dependencies.

Running the test suite

Run yarn test.

For compiling and running the tests when files change, run these commands in separate terminals:

yarn build:test --watch
yarn jest dist-test/ --watchAll


You need Python 3 to build the docs.

python3 -m venv venv
./venv/bin/pip install mkdocs-material

Run a live reloading server for the documentation:

./venv/bin/mkdocs serve

Open http://localhost:8000/ in the browser.


$ yarn version --new-version <major|minor|patch>
$ yarn publish
$ git push origin main --tags

Open https://github.com/akheron/optics-ts/releases, edit the draft release, select the newest version tag, adjust the description as needed.