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Using Node modules

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Cong Liu edited this page Mar 30, 2016 · 6 revisions

NOTE: some content in this wiki applies only to 0.12 and earlier versions. For official documentation on 0.13 and later, see http://docs.nwjs.io

There are three types of modules in Node.js:

  • internal modules (parts of Node API)

  • 3rd party modules written in JavaScript

  • 3rd party modules with C/C++ addons

All of these types can be used in node-webkit.

Note:   you may use the “Modules” page in Node's wiki or npm search to discover many open source modules.

Internal modules

The internal (built-in) modules of Node.js can be used as directly as in Node, according to the documentation on Node API.

For example, var fs = require('fs') is enough to start using the file system module.

For example, you may use the process module instantly (without any require(…)), as in Node.

And so on.

There are, however, some small changes between Node's and node-webkit's API. (See “Changes related to node” for details.)

3rd party JavaScript modules

If a 3rd party module is written totally in JavaScript (i.e. does not contain any C/C++ addons), it can be used in node-webkit the same way it is used in Node: require('moduleName').

However, the behaviour of relative paths (if such paths are used in that require() method) depends on how the parent file itself is used in your application (here “the parent file” is the file in which the require() method is called):

  • If the parent file was also required by Node (using require()), then the child's relative path is treated as relative to its parent.

  • If the parent file is included by WebKit (using any web technology: classic DOM window.open(), node-webkit's Window.open(), classic DOM XMLHttpRequest, jQuery's $.getScript(), HTML <script src="..."> element, etc.), then the child's relative path is treated as relative to the application's root directory.

The former rule means that any module's submodules are always being required exactly as in Node and work properly.

However, it is generally wise not to use the explicit relative paths (starting with ../ or ./) at all. Instead of it, just calling require('modulename') is enough — if the module has been put in the /node_modules subdirectory of your application. (See the “Loading from node_modules Folders” section of Node API.)

For example, you may install modules from npm packages by running npm install modulename in your application's directory (where your application's manifest resides), because npm would automatically put these modules in the /node_modules subdirectory.

Example: async

Here is an example of installing the async module:

$ cd /path/to/your/app
$ npm install async

Here is the resulting list of files in the whole tree:

$ find .
.
./package.json
./index.html
./node_modules
./node_modules/async
./node_modules/async/.gitmodules
./node_modules/async/package.json
./node_modules/async/Makefile
./node_modules/async/LICENSE
./node_modules/async/README.md
./node_modules/async/.npmignore
./node_modules/async/lib
./node_modules/async/lib/async.js
./node_modules/async/index.js

where your application's manifest (./package.json) might look like the following:

{
  "name": "nw-demo",
  "main": "index.html"
}

And here's an example of index.html:

<html>
<head>
<title>test</title>
<script>
var async=require('async');
</script>
</head>
<body>
test should be here.
</body>
</html>

3rd party modules with C/C++ addons

For modules containing C/C++ addons the situation is slightly different from the above — and more complex — because the ABI (application binary interface) of node-webkit differs from Node's ABI.

When such a module is installed for Node (with npm install command), npm uses its internal version of the node-gyp tool to build the addons (from their source code) for Node.js.

To build such a module for node-webkit, nw-gyp (a special fork of node-gyp) is necessary. You also have to run nw-gyp manually, because npm (being a Node's tool) does not know anything about building for node-webkit and using nw-gyp.

To install nw-gyp, run npm install nw-gyp -g.

Before actually using nw-gyp, please meet its requirements (you'll need a proper Python engine and C/C++ compiler). These requirements are not different from node-gyp's.

To build a module for node-webkit, you may at first obtain it from an npm package, as if for Node.js (npm install modulename), but then rebuild it for node-webkit (nw-gyp rebuild --target=0.5.0).

Alternatively, you may get the module's source code elsewhere (for example, from GitHub) and run nw-gyp rebuild --target=0.5.0 on it.

In both of these alternatives,

  • nw-gyp must be run in the module's directory (where the module's binding.gyp resides),

  • the necessary target version of node-webkit (such as 0.5.0 in nw-gyp rebuild --target=0.5.0) must be given explicitly, because nw-gyp cannot autodetect it,

  • you must rebuild a module before you start using it in any newer version of node-webkit, because the ABI is not stable and changes constantly with the versions. For example,

    • after node-webkit 0.6.0 is released, nw-gyp rebuild --target=0.6.0 is necessary,
    • after node-webkit 0.6.1 is released, nw-gyp rebuild --target=0.6.1 is necessary,
    • and so on.

The difference of ABI also means that the built C/C++ addons (i.e. .node files) of Node and node-webkit are mutually incompatible: you cannot use an addon in Node if it's built for node-webkit, and vice versa.

For example, you cannot use some node test.js (or npm test) to test an addon-containing module in Node if that addon has been built for node-webkit: the test will always fail (either with some cryptic error message or with a crash of the whole engine).

Important note 1:   on Windows the engine's executable file must have the name nw.exe for addons to work (i.e. you cannot rename nw.exe if you need any addon-containing modules). They use parts of the engine to sustain their execution.

Important note 2: on Windows it seems to be neccesary to include the full Python's path in the system's PATH variable.

Important note 3: Remember to replace the original .node file with your generated one, otherwise the module won't work (because it still points to the original Node.js module instead of using the one compiled for node-webkit).

For more information on that matter (including further limitations and known issues), see “Build native modules with nw-gyp”.

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