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Immutable state for React.js
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Immutable state for React.js

react-cursor hello-world in a fiddle

live demo

What is react-cursor

Cursors are a tool for working with recursive or deeply nested data, immutably. react-cursor is a javascript port of an abstraction that I first saw in ClojureScript. This implementation is decoupled from any rendering library and is very small.

Cursors are useful in UI programming, because UIs are tree shaped and naturally have tree-shaped state. Cursors let your app hold all its state in one place at the root of the UI tree; thus the root is stateful, and all downtree views are stateless.

Project Maturity

master is stable, there is a full test suite.


Cursor interface has three methods: value, swap and refine.

  • cur.value() return the value in the cursor at some path.
  • cur.refine(path, ...paths) return a cursor nested inside another cursor
  • cur.swap(f) apply f to the value in the cursor value and puts returned value into the backing store

For frequently used swap functions, see the bundled update-in dependency: see here. Cursor instances have optional syntax sugar for the swap fns provided by update-in; see CursorOperations.js


  • Cursors have value semantics, don't mutate values that come out of a cursor
  • Equal cursors are === for easy and efficient optimized rendering (see hello world jsfiddle for example)
  • You should read the source! The core cursor abstraction is 15 lines of code
  • There is an undocumented alternate implementation, RefCursor, which has reference semantics, this is only useful for working with legacy mutable code


react-cursor is governed under the MIT License.


react-cursor was built by Daniel Miladinov and Dustin Getz.

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