node-ffi/node-ffi

---

node-ffi/node-ffi.json

{
  "createdAt": "2009-12-05T17:23:17Z",
  "defaultBranch": "master",
  "description": "Node.js Foreign Function Interface",
  "fullName": "node-ffi/node-ffi",
  "homepage": "",
  "language": "JavaScript",
  "name": "node-ffi",
  "pushedAt": "2023-07-15T04:15:33Z",
  "stargazersCount": 4312,
  "topics": [],
  "updatedAt": "2025-11-23T00:38:26Z",
  "url": "https://github.com/node-ffi/node-ffi"
}

node-ffi

Node.js Foreign Function Interface

node-ffi 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: node-ffi 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.

Example

var ffi = require('ffi');

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

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

For a more detailed introduction, see the [node-ffi tutorial page][tutorial].

Requirements

• Linux, OS X, Windows, or Solaris.
• libffi comes bundled with node-ffi; it does not need to be installed on your system.
• The current version is tested to run on node v0.6, v0.8, v0.9 and v0.10.

Installation

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

$ npm install ffi

Source Install / Manual Compilation

To compile from source it’s easiest to use node-gyp:

$ npm install -g node-gyp

Now you can compile node-ffi:

$ git clone git://github.com/node-ffi/node-ffi.git
$ cd node-ffi
$ node-gyp rebuild

Types

The types that you specify in function declarations correspond to ref’s types system. So [see its docs][ref-types] 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 (FP) numbers. This is problematic because FP numbers are imprecise. To get around this, the methods in node-ffi 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.

License

MIT License. See the LICENSE file.

[v1apichanges] !: https://github.com/node-ffi/node-ffi/wiki/API-changes-from-v0.x-to-v1.x [tutorial] !: https://github.com/node-ffi/node-ffi/wiki/Node-FFI-Tutorial [ref-types] !: https://github.com/TooTallNate/ref#built-in-types