Craig Condon
619 lines
24 KiB
HTML
619 lines
24 KiB
HTML
<!doctype html>
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<title>Modules Node.js v0.8.14 Manual & Documentation</title>
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<div id="column1" class="interior">
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<header>
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<h1>Node.js v0.8.14 Manual & Documentation</h1>
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<div id="gtoc">
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<p>
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<a href="index.html" name="toc">Index</a> |
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<a href="all.html">View on single page</a> |
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<a href="modules.json">View as JSON</a>
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</p>
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</div>
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<hr>
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</header>
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<div id="toc">
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<h2>Table of Contents</h2>
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<ul>
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<li><a href="#modules_modules">Modules</a><ul>
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<li><a href="#modules_cycles">Cycles</a></li>
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<li><a href="#modules_core_modules">Core Modules</a></li>
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<li><a href="#modules_file_modules">File Modules</a></li>
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<li><a href="#modules_loading_from_node_modules_folders">Loading from <code>node_modules</code> Folders</a></li>
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<li><a href="#modules_folders_as_modules">Folders as Modules</a></li>
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<li><a href="#modules_caching">Caching</a><ul>
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<li><a href="#modules_module_caching_caveats">Module Caching Caveats</a></li>
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</ul>
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</li>
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<li><a href="#modules_the_module_object">The <code>module</code> Object</a><ul>
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<li><a href="#modules_module_exports">module.exports</a></li>
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<li><a href="#modules_module_require_id">module.require(id)</a></li>
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<li><a href="#modules_module_id">module.id</a></li>
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<li><a href="#modules_module_filename">module.filename</a></li>
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<li><a href="#modules_module_loaded">module.loaded</a></li>
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<li><a href="#modules_module_parent">module.parent</a></li>
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<li><a href="#modules_module_children">module.children</a></li>
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</ul>
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</li>
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<li><a href="#modules_all_together">All Together...</a></li>
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<li><a href="#modules_loading_from_the_global_folders">Loading from the global folders</a></li>
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<li><a href="#modules_accessing_the_main_module">Accessing the main module</a></li>
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<li><a href="#modules_addenda_package_manager_tips">Addenda: Package Manager Tips</a></li>
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</ul>
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</li>
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</ul>
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</div>
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<div id="apicontent">
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<h1>Modules<span><a class="mark" href="#modules_modules" id="modules_modules">#</a></span></h1>
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<pre><code>Stability: 5 - Locked</code></pre>
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<!--name=module-->
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<p>Node has a simple module loading system. In Node, files and modules are in
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one-to-one correspondence. As an example, <code>foo.js</code> loads the module
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<code>circle.js</code> in the same directory.
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</p>
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<p>The contents of <code>foo.js</code>:
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</p>
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<pre><code>var circle = require('./circle.js');
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console.log( 'The area of a circle of radius 4 is '
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+ circle.area(4));</code></pre>
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<p>The contents of <code>circle.js</code>:
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</p>
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<pre><code>var PI = Math.PI;
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exports.area = function (r) {
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return PI * r * r;
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};
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exports.circumference = function (r) {
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return 2 * PI * r;
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};</code></pre>
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<p>The module <code>circle.js</code> has exported the functions <code>area()</code> and
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<code>circumference()</code>. To export an object, add to the special <code>exports</code>
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object.
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</p>
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<p>Variables
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local to the module will be private. In this example the variable <code>PI</code> is
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private to <code>circle.js</code>.
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</p>
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<p>The module system is implemented in the <code>require("module")</code> module.
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</p>
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<h2>Cycles<span><a class="mark" href="#modules_cycles" id="modules_cycles">#</a></span></h2>
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<!--type=misc-->
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<p>When there are circular <code>require()</code> calls, a module might not be
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done being executed when it is returned.
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</p>
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<p>Consider this situation:
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</p>
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<p><code>a.js</code>:
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</p>
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<pre><code>console.log('a starting');
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exports.done = false;
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var b = require('./b.js');
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console.log('in a, b.done = %j', b.done);
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exports.done = true;
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console.log('a done');</code></pre>
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<p><code>b.js</code>:
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</p>
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<pre><code>console.log('b starting');
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exports.done = false;
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var a = require('./a.js');
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console.log('in b, a.done = %j', a.done);
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exports.done = true;
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console.log('b done');</code></pre>
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<p><code>main.js</code>:
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</p>
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<pre><code>console.log('main starting');
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var a = require('./a.js');
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var b = require('./b.js');
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console.log('in main, a.done=%j, b.done=%j', a.done, b.done);</code></pre>
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<p>When <code>main.js</code> loads <code>a.js</code>, then <code>a.js</code> in turn loads <code>b.js</code>. At that
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point, <code>b.js</code> tries to load <code>a.js</code>. In order to prevent an infinite
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loop an <strong>unfinished copy</strong> of the <code>a.js</code> exports object is returned to the
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<code>b.js</code> module. <code>b.js</code> then finishes loading, and its exports object is
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provided to the <code>a.js</code> module.
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</p>
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<p>By the time <code>main.js</code> has loaded both modules, they're both finished.
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The output of this program would thus be:
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</p>
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<pre><code>$ node main.js
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main starting
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a starting
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b starting
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in b, a.done = false
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b done
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in a, b.done = true
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a done
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in main, a.done=true, b.done=true</code></pre>
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<p>If you have cyclic module dependencies in your program, make sure to
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plan accordingly.
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</p>
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<h2>Core Modules<span><a class="mark" href="#modules_core_modules" id="modules_core_modules">#</a></span></h2>
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<!--type=misc-->
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<p>Node has several modules compiled into the binary. These modules are
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described in greater detail elsewhere in this documentation.
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</p>
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<p>The core modules are defined in node's source in the <code>lib/</code> folder.
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</p>
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<p>Core modules are always preferentially loaded if their identifier is
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passed to <code>require()</code>. For instance, <code>require('http')</code> will always
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return the built in HTTP module, even if there is a file by that name.
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</p>
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<h2>File Modules<span><a class="mark" href="#modules_file_modules" id="modules_file_modules">#</a></span></h2>
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<!--type=misc-->
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<p>If the exact filename is not found, then node will attempt to load the
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required filename with the added extension of <code>.js</code>, <code>.json</code>, and then <code>.node</code>.
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</p>
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<p><code>.js</code> files are interpreted as JavaScript text files, and <code>.json</code> files are
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parsed as JSON text files. <code>.node</code> files are interpreted as compiled addon
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modules loaded with <code>dlopen</code>.
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</p>
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<p>A module prefixed with <code>'/'</code> is an absolute path to the file. For
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example, <code>require('/home/marco/foo.js')</code> will load the file at
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<code>/home/marco/foo.js</code>.
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</p>
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<p>A module prefixed with <code>'./'</code> is relative to the file calling <code>require()</code>.
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That is, <code>circle.js</code> must be in the same directory as <code>foo.js</code> for
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<code>require('./circle')</code> to find it.
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</p>
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<p>Without a leading '/' or './' to indicate a file, the module is either a
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"core module" or is loaded from a <code>node_modules</code> folder.
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</p>
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<p>If the given path does not exist, <code>require()</code> will throw an Error with its
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<code>code</code> property set to <code>'MODULE_NOT_FOUND'</code>.
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</p>
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<h2>Loading from <code>node_modules</code> Folders<span><a class="mark" href="#modules_loading_from_node_modules_folders" id="modules_loading_from_node_modules_folders">#</a></span></h2>
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<!--type=misc-->
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<p>If the module identifier passed to <code>require()</code> is not a native module,
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and does not begin with <code>'/'</code>, <code>'../'</code>, or <code>'./'</code>, then node starts at the
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parent directory of the current module, and adds <code>/node_modules</code>, and
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attempts to load the module from that location.
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</p>
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<p>If it is not found there, then it moves to the parent directory, and so
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on, until the root of the tree is reached.
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</p>
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<p>For example, if the file at <code>'/home/ry/projects/foo.js'</code> called
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<code>require('bar.js')</code>, then node would look in the following locations, in
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this order:
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</p>
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<ul>
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<li><code>/home/ry/projects/node_modules/bar.js</code></li>
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<li><code>/home/ry/node_modules/bar.js</code></li>
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<li><code>/home/node_modules/bar.js</code></li>
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<li><code>/node_modules/bar.js</code></li>
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</ul>
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<p>This allows programs to localize their dependencies, so that they do not
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clash.
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</p>
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<h2>Folders as Modules<span><a class="mark" href="#modules_folders_as_modules" id="modules_folders_as_modules">#</a></span></h2>
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<!--type=misc-->
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<p>It is convenient to organize programs and libraries into self-contained
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directories, and then provide a single entry point to that library.
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There are three ways in which a folder may be passed to <code>require()</code> as
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an argument.
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</p>
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<p>The first is to create a <code>package.json</code> file in the root of the folder,
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which specifies a <code>main</code> module. An example package.json file might
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look like this:
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</p>
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<pre><code>{ "name" : "some-library",
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"main" : "./lib/some-library.js" }</code></pre>
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<p>If this was in a folder at <code>./some-library</code>, then
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<code>require('./some-library')</code> would attempt to load
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<code>./some-library/lib/some-library.js</code>.
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</p>
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<p>This is the extent of Node's awareness of package.json files.
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</p>
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<p>If there is no package.json file present in the directory, then node
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will attempt to load an <code>index.js</code> or <code>index.node</code> file out of that
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directory. For example, if there was no package.json file in the above
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example, then <code>require('./some-library')</code> would attempt to load:
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</p>
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<ul>
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<li><code>./some-library/index.js</code></li>
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<li><code>./some-library/index.node</code></li>
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</ul>
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<h2>Caching<span><a class="mark" href="#modules_caching" id="modules_caching">#</a></span></h2>
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<!--type=misc-->
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<p>Modules are cached after the first time they are loaded. This means
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(among other things) that every call to <code>require('foo')</code> will get
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exactly the same object returned, if it would resolve to the same file.
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</p>
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<p>Multiple calls to <code>require('foo')</code> may not cause the module code to be
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executed multiple times. This is an important feature. With it,
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"partially done" objects can be returned, thus allowing transitive
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dependencies to be loaded even when they would cause cycles.
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</p>
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<p>If you want to have a module execute code multiple times, then export a
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function, and call that function.
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</p>
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<h3>Module Caching Caveats<span><a class="mark" href="#modules_module_caching_caveats" id="modules_module_caching_caveats">#</a></span></h3>
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<!--type=misc-->
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<p>Modules are cached based on their resolved filename. Since modules may
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resolve to a different filename based on the location of the calling
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module (loading from <code>node_modules</code> folders), it is not a <em>guarantee</em>
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that <code>require('foo')</code> will always return the exact same object, if it
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would resolve to different files.
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</p>
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<h2>The <code>module</code> Object<span><a class="mark" href="#modules_the_module_object" id="modules_the_module_object">#</a></span></h2>
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<!-- type=var -->
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<!-- name=module -->
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<ul>
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<li>{Object}</li>
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</ul>
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<p>In each module, the <code>module</code> free variable is a reference to the object
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representing the current module. In particular
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<code>module.exports</code> is the same as the <code>exports</code> object.
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<code>module</code> isn't actually a global but rather local to each module.
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</p>
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<h3>module.exports<span><a class="mark" href="#modules_module_exports" id="modules_module_exports">#</a></span></h3>
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<div class="signature"><ul>
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<li><span class="type">Object</span></li>
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</div></ul>
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<p>The <code>exports</code> object is created by the Module system. Sometimes this is not
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acceptable, many want their module to be an instance of some class. To do this
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assign the desired export object to <code>module.exports</code>. For example suppose we
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were making a module called <code>a.js</code>
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</p>
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<pre><code>var EventEmitter = require('events').EventEmitter;
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module.exports = new EventEmitter();
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// Do some work, and after some time emit
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// the 'ready' event from the module itself.
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setTimeout(function() {
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module.exports.emit('ready');
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}, 1000);</code></pre>
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<p>Then in another file we could do
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</p>
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<pre><code>var a = require('./a');
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a.on('ready', function() {
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console.log('module a is ready');
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});</code></pre>
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<p>Note that assignment to <code>module.exports</code> must be done immediately. It cannot be
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done in any callbacks. This does not work:
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</p>
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<p>x.js:
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</p>
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<pre><code>setTimeout(function() {
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module.exports = { a: "hello" };
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}, 0);</code></pre>
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<p>y.js:
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</p>
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<pre><code>var x = require('./x');
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console.log(x.a);</code></pre>
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|
<h3>module.require(id)<span><a class="mark" href="#modules_module_require_id" id="modules_module_require_id">#</a></span></h3>
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<div class="signature"><ul>
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<li><code>id</code> <span class="type">String</span></li>
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<li>Return: <span class="type">Object</span> <code>exports</code> from the resolved module</li>
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</div></ul>
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<p>The <code>module.require</code> method provides a way to load a module as if
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<code>require()</code> was called from the original module.
|
|
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</p>
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<p>Note that in order to do this, you must get a reference to the <code>module</code>
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object. Since <code>require()</code> returns the <code>exports</code>, and the <code>module</code> is
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typically <em>only</em> available within a specific module's code, it must be
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explicitly exported in order to be used.
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|
|
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</p>
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|
<h3>module.id<span><a class="mark" href="#modules_module_id" id="modules_module_id">#</a></span></h3>
|
|
<div class="signature"><ul>
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|
<li><span class="type">String</span></li>
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</div></ul>
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<p>The identifier for the module. Typically this is the fully resolved
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filename.
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|
|
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</p>
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|
<h3>module.filename<span><a class="mark" href="#modules_module_filename" id="modules_module_filename">#</a></span></h3>
|
|
<div class="signature"><ul>
|
|
<li><span class="type">String</span></li>
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</div></ul>
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<p>The fully resolved filename to the module.
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|
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</p>
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|
<h3>module.loaded<span><a class="mark" href="#modules_module_loaded" id="modules_module_loaded">#</a></span></h3>
|
|
<div class="signature"><ul>
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<li><span class="type">Boolean</span></li>
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</div></ul>
|
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<p>Whether or not the module is done loading, or is in the process of
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loading.
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|
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</p>
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<h3>module.parent<span><a class="mark" href="#modules_module_parent" id="modules_module_parent">#</a></span></h3>
|
|
<div class="signature"><ul>
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|
<li><span class="type">Module Object</span></li>
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</div></ul>
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|
<p>The module that required this one.
|
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|
|
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</p>
|
|
<h3>module.children<span><a class="mark" href="#modules_module_children" id="modules_module_children">#</a></span></h3>
|
|
<div class="signature"><ul>
|
|
<li><span class="type">Array</span></li>
|
|
</div></ul>
|
|
<p>The module objects required by this one.
|
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|
|
|
|
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</p>
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<h2>All Together...<span><a class="mark" href="#modules_all_together" id="modules_all_together">#</a></span></h2>
|
|
<!-- type=misc -->
|
|
|
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<p>To get the exact filename that will be loaded when <code>require()</code> is called, use
|
|
the <code>require.resolve()</code> function.
|
|
|
|
</p>
|
|
<p>Putting together all of the above, here is the high-level algorithm
|
|
in pseudocode of what require.resolve does:
|
|
|
|
</p>
|
|
<pre><code>require(X) from module at path Y
|
|
1. If X is a core module,
|
|
a. return the core module
|
|
b. STOP
|
|
2. If X begins with './' or '/' or '../'
|
|
a. LOAD_AS_FILE(Y + X)
|
|
b. LOAD_AS_DIRECTORY(Y + X)
|
|
3. LOAD_NODE_MODULES(X, dirname(Y))
|
|
4. THROW "not found"
|
|
|
|
LOAD_AS_FILE(X)
|
|
1. If X is a file, load X as JavaScript text. STOP
|
|
2. If X.js is a file, load X.js as JavaScript text. STOP
|
|
3. If X.node is a file, load X.node as binary addon. STOP
|
|
|
|
LOAD_AS_DIRECTORY(X)
|
|
1. If X/package.json is a file,
|
|
a. Parse X/package.json, and look for "main" field.
|
|
b. let M = X + (json main field)
|
|
c. LOAD_AS_FILE(M)
|
|
2. If X/index.js is a file, load X/index.js as JavaScript text. STOP
|
|
3. If X/index.node is a file, load X/index.node as binary addon. STOP
|
|
|
|
LOAD_NODE_MODULES(X, START)
|
|
1. let DIRS=NODE_MODULES_PATHS(START)
|
|
2. for each DIR in DIRS:
|
|
a. LOAD_AS_FILE(DIR/X)
|
|
b. LOAD_AS_DIRECTORY(DIR/X)
|
|
|
|
NODE_MODULES_PATHS(START)
|
|
1. let PARTS = path split(START)
|
|
2. let ROOT = index of first instance of "node_modules" in PARTS, or 0
|
|
3. let I = count of PARTS - 1
|
|
4. let DIRS = []
|
|
5. while I > ROOT,
|
|
a. if PARTS[I] = "node_modules" CONTINUE
|
|
c. DIR = path join(PARTS[0 .. I] + "node_modules")
|
|
b. DIRS = DIRS + DIR
|
|
c. let I = I - 1
|
|
6. return DIRS</code></pre>
|
|
<h2>Loading from the global folders<span><a class="mark" href="#modules_loading_from_the_global_folders" id="modules_loading_from_the_global_folders">#</a></span></h2>
|
|
<!-- type=misc -->
|
|
|
|
<p>If the <code>NODE_PATH</code> environment variable is set to a colon-delimited list
|
|
of absolute paths, then node will search those paths for modules if they
|
|
are not found elsewhere. (Note: On Windows, <code>NODE_PATH</code> is delimited by
|
|
semicolons instead of colons.)
|
|
|
|
</p>
|
|
<p>Additionally, node will search in the following locations:
|
|
|
|
</p>
|
|
<ul>
|
|
<li>1: <code>$HOME/.node_modules</code></li>
|
|
<li>2: <code>$HOME/.node_libraries</code></li>
|
|
<li>3: <code>$PREFIX/lib/node</code></li>
|
|
</ul>
|
|
<p>Where <code>$HOME</code> is the user's home directory, and <code>$PREFIX</code> is node's
|
|
configured <code>node_prefix</code>.
|
|
|
|
</p>
|
|
<p>These are mostly for historic reasons. You are highly encouraged to
|
|
place your dependencies locally in <code>node_modules</code> folders. They will be
|
|
loaded faster, and more reliably.
|
|
|
|
</p>
|
|
<h2>Accessing the main module<span><a class="mark" href="#modules_accessing_the_main_module" id="modules_accessing_the_main_module">#</a></span></h2>
|
|
<!-- type=misc -->
|
|
|
|
<p>When a file is run directly from Node, <code>require.main</code> is set to its
|
|
<code>module</code>. That means that you can determine whether a file has been run
|
|
directly by testing
|
|
|
|
</p>
|
|
<pre><code>require.main === module</code></pre>
|
|
<p>For a file <code>foo.js</code>, this will be <code>true</code> if run via <code>node foo.js</code>, but
|
|
<code>false</code> if run by <code>require('./foo')</code>.
|
|
|
|
</p>
|
|
<p>Because <code>module</code> provides a <code>filename</code> property (normally equivalent to
|
|
<code>__filename</code>), the entry point of the current application can be obtained
|
|
by checking <code>require.main.filename</code>.
|
|
|
|
</p>
|
|
<h2>Addenda: Package Manager Tips<span><a class="mark" href="#modules_addenda_package_manager_tips" id="modules_addenda_package_manager_tips">#</a></span></h2>
|
|
<!-- type=misc -->
|
|
|
|
<p>The semantics of Node's <code>require()</code> function were designed to be general
|
|
enough to support a number of sane directory structures. Package manager
|
|
programs such as <code>dpkg</code>, <code>rpm</code>, and <code>npm</code> will hopefully find it possible to
|
|
build native packages from Node modules without modification.
|
|
|
|
</p>
|
|
<p>Below we give a suggested directory structure that could work:
|
|
|
|
</p>
|
|
<p>Let's say that we wanted to have the folder at
|
|
<code>/usr/lib/node/<some-package>/<some-version></code> hold the contents of a
|
|
specific version of a package.
|
|
|
|
</p>
|
|
<p>Packages can depend on one another. In order to install package <code>foo</code>, you
|
|
may have to install a specific version of package <code>bar</code>. The <code>bar</code> package
|
|
may itself have dependencies, and in some cases, these dependencies may even
|
|
collide or form cycles.
|
|
|
|
</p>
|
|
<p>Since Node looks up the <code>realpath</code> of any modules it loads (that is,
|
|
resolves symlinks), and then looks for their dependencies in the
|
|
<code>node_modules</code> folders as described above, this situation is very simple to
|
|
resolve with the following architecture:
|
|
|
|
</p>
|
|
<ul>
|
|
<li><code>/usr/lib/node/foo/1.2.3/</code> - Contents of the <code>foo</code> package, version 1.2.3.</li>
|
|
<li><code>/usr/lib/node/bar/4.3.2/</code> - Contents of the <code>bar</code> package that <code>foo</code>
|
|
depends on.</li>
|
|
<li><code>/usr/lib/node/foo/1.2.3/node_modules/bar</code> - Symbolic link to
|
|
<code>/usr/lib/node/bar/4.3.2/</code>.</li>
|
|
<li><code>/usr/lib/node/bar/4.3.2/node_modules/*</code> - Symbolic links to the packages
|
|
that <code>bar</code> depends on.</li>
|
|
</ul>
|
|
<p>Thus, even if a cycle is encountered, or if there are dependency
|
|
conflicts, every module will be able to get a version of its dependency
|
|
that it can use.
|
|
|
|
</p>
|
|
<p>When the code in the <code>foo</code> package does <code>require('bar')</code>, it will get the
|
|
version that is symlinked into <code>/usr/lib/node/foo/1.2.3/node_modules/bar</code>.
|
|
Then, when the code in the <code>bar</code> package calls <code>require('quux')</code>, it'll get
|
|
the version that is symlinked into
|
|
<code>/usr/lib/node/bar/4.3.2/node_modules/quux</code>.
|
|
|
|
</p>
|
|
<p>Furthermore, to make the module lookup process even more optimal, rather
|
|
than putting packages directly in <code>/usr/lib/node</code>, we could put them in
|
|
<code>/usr/lib/node_modules/<name>/<version></code>. Then node will not bother
|
|
looking for missing dependencies in <code>/usr/node_modules</code> or <code>/node_modules</code>.
|
|
|
|
</p>
|
|
<p>In order to make modules available to the node REPL, it might be useful to
|
|
also add the <code>/usr/lib/node_modules</code> folder to the <code>$NODE_PATH</code> environment
|
|
variable. Since the module lookups using <code>node_modules</code> folders are all
|
|
relative, and based on the real path of the files making the calls to
|
|
<code>require()</code>, the packages themselves can be anywhere.
|
|
</p>
|
|
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