npm i lean-client-js-browser


Interface to the Lean server

by leanprover

3.3.1 (see all)License:Apache-2.0TypeScript:Built-In
npm i lean-client-js-browser


This is a JavaScript library to interface with the server mode of the Lean theorem prover.

This package contains the web browser version. It communicates with an Emscripten build of Lean in a WebWorker, using WebAssembly if available.

How to use

You will need to place the files from the Lean Emscripten build (downloadable from here, see the lean-*-browser.zip files) and a suitable .zip bundle of .olean files (see instructions here) into a subdirectory of this directory called dist/ for the demo files to work. The library.zip file is cached in IndexedDB to save on downloading, provided that its associated library.info.json is present at the same path.

The main class is WebWorkerTransport. The constructor takes a LeanJsOptions object with the following fields:

  • libraryZip: URL to library.zip. Must end in .zip. This field is used to generate the default values for some of the optional fields below.
  • libraryMeta (optional): URL to library.info.json, a JSON file whose keys are the Lean packages contained in library.zip and whose values are URL prefixes that point to the Lean source files. (default: the value of libraryZip with the final .zip replaced with .info.json)
  • libraryOleanMap (optional): URL to library.olean_map.json, a JSON file whose keys are the filenames of the oleans in library.zip (with .olean removed) and whose values are the name of the Lean package that they originate from (default: the value of libraryZip with the final .zip replaced with .olean_map.json)
  • libraryKey (optional): name for the key used in the indexedDB cache (default: the filename of libraryZip with .zip removed)
  • At least one of javascript or (webassemblyWasm + webassemblyJs) must be provided:
    • javascript: URL to lean_js_js.js
    • Both of the following fields should be provided to use the WebAssembly version of the Lean server:
      • webassemblyWasm: URL to lean_js_wasm.wasm
      • webassemblyJs: URL to lean_js_wasm.js
  • memoryMB (optional): size of memory in MB provided (default: 256)
  • dbName (optional): name of the IndexedDB database used to cache (default: leanlibrary)

The WebWorkerTransport object that is returned should be passed to the Server constructor. See the lean-client-js library for more information about the Server class.

See demo.ts for an example on how to use this package in a TypeScript project. After building, see dist/lib_test.html for how to use this package in a webpage.

See leanprover-community/lean-web-editor and mpedramfar/Lean-game-maker for example TypeScript projects that use this library.

See these Observable notebooks for example webpages that use the UMD module leanBrowser.js.


To build the demo file, follow the directions in the README file in the parent package lean-client-js. The demo file will be written to dist/demo.html.

Running ../node_modules/.bin/webpack or npm run build from this directory will build and output the test file dist/lib_test.html as well as a UMD module dist/leanBrowser.js for use in webpages.

Once the files are built, you can check them out by starting a local web server (from the dist/ directory) and navigating to /index.html or /lib_test.html.

Changes in v2.0.0

This version of lean-client-js-browser has two main differences from versions before v2.0.0:

  1. First, it removes the BrowserInProcessTransport class which allowed running the Lean Emscripten server in the browser's main thread. You must use WebWorkerTransport, which runs the server in a WebWorker.

  2. Second, it caches the library.zip file in the browser's IndexedDB store. The database name is determined by opts.dbName. This DB contains two "Object stores", one named library and one named meta:

  • meta is a key-value store, where the key used is given by opts.libName and the values are JSON objects which map the Lean package names in the ZIP file to source links
  • library is another key-value store, where the keys are the same as in meta and the values are the ZIP files stored as binary blobs.



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