vim.wasm - 基于 WebAssembly 实现 vim

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This project is an experimental fork of Vim editor by @rhysd to compile it into WebAssembly using emscripten and binaryen.

Try it with your browser

    • Please access from a desktop browser (Chrome/Firefox/Safari/Edge). Safari seems the best on macOS.
    • Please avoid slow networks. Your browser will fetch total of around 1MB files.
    • vim.wasm takes key inputs from DOM keydown event. Please disable your browser extensions which affect key inputs (incognito mode would be the best).
    • This project is very early phase of experiment. Currently only tiny features are supported. More features will be implemented (please see TODO section). And you may notice soon on trying it... it's buggy :)
    • If inputting something does not change anything, please try to click somewhere in the page. Vim may have lost the focus.
    • You can try vimtutor by :e tutor.
    • Vim exits on :quit, but the command does not close a browser tab. Please close it manually :)

The goal of this project is running Vim editor on browser by compiling Vim C sources into WebAssembly.

My Japanese Blogpost

Main Screen

How It Works

Build Process

Build Process

WebAssembly frontend for Vim is implemented as a new GUI frontend. C sources are compiled to each LLVM bitcode files and then they are linked to one bitcode file vim.bc by emcc. emcc finally compiles the vim.bc into vim.wasm binary using binaryen and generates HTML/JavaScript runtime.

The difference I faced at first was the lack of terminal library such as ncurses. I modified configure script to ignore the terminal library check. It's OK since GUI frontend for Wasm is always used instead of CUI frontend. I needed many workarounds to pass configure checks.

emscripten provides Unix-like environment. So os_unix.c can support Wasm. However, some features are not supported by emscripten. I added many #ifdef FEAT_GUI_WASM guards to disable features which cannot be supported by Wasm (i.e. fork (2) support, PTY support, signal handlers are stubbed, ...etc).

I created gui_wasm.c heavily referencing gui_mac.c and gui_w32.c. Event loop (gui_mch_update() and gui_mch_wait_for_chars()) is simply implemented with sleep(). And almost all UI rendering events arer passed to JavaScript layer by calling JavaScript functions from C thanks to emscripten.

C sources are compiled (with many optimizations) into LLVM bitcode with Clang which is integrated to emscripten. Then all bitcode files (.o) are linked to one bitcode file vim.bc with llvm-link linker (also integrated to emscripten).

Finally I created JavaScript runtime to draw the rendering events sent from C. It is created as wasm/runtime.ts using emscripten API. It draws Vim screen to <canvas/> element with rendering events such as 'draw text', 'scroll screen', 'set foreground color', 'clear rect', ...etc.

emcc (emscripten's C compiler) compiles the vim.bc into vim.wasm, vim.js and vim.html with preloaded Vim runtime files (i.e. colorscheme) using binaryen. Runtime files are put on a virtual file system provided by emscripten on a browser.

Now hosting vim.html with a web server and accessing to it with browser opens Vim. It works.

User Interaction

User Interaction

User interaction is very simple. You input something with keyboard. Browser takes it as KeyboardEvent on keydown event and JavaScript runtime sends the input to Wasm thanks to emscripten's JS to C API. Sent input is added to a buffer in C layer. It affects the editor's state.

An editor core implemented in C calculates rendering events and sends it to JavaScript layer thanks to emscripten's C to JS API. JavaScript runtime receives rendering events and stores them into a queue. On animation frames, it draws them to <canvas/> element in the web page.

Finally you can see the rendered results in the page.


Please make sure that Emscripten and binaryen (I'm using 1.38.6) are installed. If you use macOS, they can be installed with brew install emscripten binaryen.

You can use script to hack this project. Just after cloning this repository, simply run ./ and it builds vim.wasm in wasm/ directory. It takes time and CPU power a lot.

Finally host the wasm/ directly on localhost with web server such as python -m http.server 1234. Accessing to localhost:1234/vim.html will start Vim with debug build. Note that it's much slower than release build since many debug features are enabled.

Please note that this repository's wasm branch is frequently rebased on the latest vim/vim master branch. If you want to hack this project, please ensure to create your own branch and merge wasm branch into your branch by git merge.

Known Issues

  • WebAssembly nor JavaScript does not provide sleep(). By default, emscripten compiles sleep() into a busy loop. So vim.wasm is using Emterpreter which provides emscripten_sleep(). Some whitelisted functions are run with Emterpreter. But this feature is not so stable. It makes built binaries larger and compilation longer.
  • JavaScript to C does not fully work with Emterpreter. For example, calling some C APIs breaks Emterpreter stack. This also means that calling C functions from JavaScript passing a string parameter does not work.


Development is managed in GitHub Projects.

  • 'small' (or larger) features support (currently only 'tiny' features are supported)
  • Async event loop (to disable Emterpreter)
  • Mouse support
  • Persistent .vimrc
  • Packaging vim.wasm as npm package or ES Modules as Web Component
  • Save files to local on :write

Special Thanks

This project was heavily inspired by impressive project vim.js by Lu Wang.


All additional files in this repository are licensed under the same license as Vim (VIM LICENSE). Please see :help license for more detail.

Original README is following.

Vim Logo

What is Vim?

Vim is a greatly improved version of the good old UNIX editor Vi. Many new features have been added: multi-level undo, syntax highlighting, command line history, on-line help, spell checking, filename completion, block operations, script language, etc. There is also a Graphical User Interface (GUI) available. Still, Vi compatibility is maintained, those who have Vi "in the fingers" will feel at home. See runtime/doc/vi_diff.txt for differences with Vi.

This editor is very useful for editing programs and other plain text files. All commands are given with normal keyboard characters, so those who can type with ten fingers can work very fast. Additionally, function keys can be mapped to commands by the user, and the mouse can be used.

Vim runs under MS-Windows (NT, 2000, XP, Vista, 7, 8, 10), Macintosh, VMS and almost all flavours of UNIX. Porting to other systems should not be very difficult. Older versions of Vim run on MS-DOS, MS-Windows 95/98/Me, Amiga DOS, Atari MiNT, BeOS, RISC OS and OS/2. These are no longer maintained.


You can often use your favorite package manager to install Vim. On Mac and Linux a small version of Vim is pre-installed, you still need to install Vim if you want more features.

There are separate distributions for Unix, PC, Amiga and some other systems. This file comes with the runtime archive. It includes the documentation, syntax files and other files that are used at runtime. To run Vim you must get either one of the binary archives or a source archive. Which one you need depends on the system you want to run it on and whether you want or must compile it yourself. Check… for an overview of currently available distributions.

Some popular places to get the latest Vim:


If you obtained a binary distribution you don't need to compile Vim. If you obtained a source distribution, all the stuff for compiling Vim is in the src directory. See src/INSTALL for instructions.


See one of these files for system-specific instructions. Either in the READMEdir directory (in the repository) or the top directory (if you unpack an archive):

README_ami.txt		Amiga
README_unix.txt		Unix
README_dos.txt		MS-DOS and MS-Windows
README_mac.txt		Macintosh
README_vms.txt		VMS

There are other README_*.txt files, depending on the distribution you used.


The Vim tutor is a one hour training course for beginners. Often it can be started as vimtutor. See :help tutor for more information.

The best is to use :help in Vim. If you don't have an executable yet, read runtime/doc/help.txt. It contains pointers to the other documentation files. The User Manual reads like a book and is recommended to learn to use Vim. See :help user-manual.


Vim is Charityware. You can use and copy it as much as you like, but you are encouraged to make a donation to help orphans in Uganda. Please read the file runtime/doc/uganda.txt for details (do :help uganda inside Vim).

Summary of the license: There are no restrictions on using or distributing an unmodified copy of Vim. Parts of Vim may also be distributed, but the license text must always be included. For modified versions a few restrictions apply. The license is GPL compatible, you may compile Vim with GPL libraries and distribute it.


Fixing bugs and adding new features takes a lot of time and effort. To show your appreciation for the work and motivate Bram and others to continue working on Vim please send a donation.

Since Bram is back to a paid job the money will now be used to help children in Uganda. See runtime/doc/uganda.txt. But at the same time donations increase Bram's motivation to keep working on Vim!

For the most recent information about sponsoring look on the Vim web site:


If you would like to help making Vim better, see the file.


The latest news about Vim can be found on the Vim home page:

If you have problems, have a look at the Vim documentation or tips:…

If you still have problems or any other questions, use one of the mailing lists to discuss them with Vim users and developers:…

If nothing else works, report bugs directly: Bram Moolenaar

Main author

Send any other comments, patches, flowers and suggestions to: Bram Moolenaar

This is for version 8.1 of Vim: Vi IMproved.