Naughty Program Manipulator

    DefinitelyTyped icon, indicating that this package has TypeScript declarations provided by the separate @types/ffi package

    2.3.0 • Public • Published


    Node.js Foreign Function Interface

    Build Status Build Status

    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.


    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.


    • 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.


    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://
    $ cd node-ffi
    $ node-gyp rebuild


    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 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.


    MIT License. See the LICENSE file.


    npm i ffi

    DownloadsWeekly Downloads






    Unpacked Size

    3.88 MB

    Total Files


    Last publish


    • tootallnate