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5.0.11 • Public • Published


Foreign Function Interface for JavaScript(NodeJS/QuickJS)

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js-ffi-cross is a Node.js addon for loading and calling dynamic libraries using pure JavaScript. It can be used to create bindings to native libraries without writing any C++ code.

It also simplifies the augmentation of node.js with C code as it takes care of handling the translation of types across JavaScript and C, which can add reams of boilerplate code to your otherwise simple C. See the example/factorial for an example of this use case.

WARNING: js-ffi-cross assumes you know what you're doing. You can pretty easily create situations where you will segfault the interpreter and unless you've got C debugger skills, you probably won't know what's going on.

WARNING: As a fork of node-ffi and node-ffi-napi, the original API of node-ffi is are rewrited in the js-ffs-cross. So please reference the TypeScript DefinitelyTyped file. The API did not have very well-defined properties in the context of garbage collection and multi-threaded execution. It is recommended to avoid any multi-threading usage of this library if possible.


const ffi = require('ffi-cross');

const libm = ffi.Library('libm', {
  'ceil': [ ffi.types.double [ ffi.types.double ] ]
libm.ceil(1.5); // 2

// You can also access just functions in the current process by passing a null
const current = ffi.Library(null, {
  'atoi': [ ffi.types.int, [ ffi.types.CString ] ]
current.atoi('1234'); // 1234

For a more detailed introduction, see the js-ffi-cross tutorial page.


  • Linux, OS X, Windows, or Solaris.
  • libffi comes bundled with js-ffi-cross; it does not need to be installed on your system.
  • The current version is tested to run on Node 12 and above.


Make sure you've installed all the necessary build tools for your platform, then invoke:

npm install ffi-cross

Source Install / Manual Compilation

Now you can compile js-ffi-cross:

git clone git://github.com/ffi-cross/js-ffi-cross.git
cd js-ffi-cross
npm i
npm run prebuild

Building debug version:

npm run prebuild:debug


On Win32, should install chocolatey and sqlite3 with Administrator permission powershell

Set-ExecutionPolicy Bypass -Scope Process -Force; [System.Net.ServicePointManager]::SecurityProtocol = [System.Net.ServicePointManager]::SecurityProtocol -bor 3072; iex ((New-Object System.Net.WebClient).DownloadString('https://chocolatey.org/install.ps1'))
choco install -y --no-progress sqlite

On Debian and decendent Linux, should install sqlite3 with:

sudo apt-get install -y libsqlite3-dev


The types that you specify in function declarations correspond to ref's types system. So see its docs for a reference if you are unfamiliar.

V8 and 64-bit Types

Internally, V8 stores integers that will fit into a 32-bit space in a 32-bit integer, and those that fall outside of this get put into double-precision floating point numbers. This is problematic because FP numbers are imprecise. To get around this, the methods in js-ffi-cross that deal with 64-bit integers return strings and can accept strings as parameters.

Call Overhead

There is non-trivial overhead associated with FFI calls. Comparing a hard-coded binding version of strtoul() to an FFI version of strtoul() shows that the native hard-coded binding is orders of magnitude faster. So don't just use the C version of a function just because it's faster. There's a significant cost in FFI calls, so make them worth it.


MIT License. See the LICENSE file.

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