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<!--replace-end-7--><!--replace-end-4--><!--replace-end-1--></head><body><div class="ui fluid container universe"><!--replace-start-2--><!--replace-start-3--><!--replace-start-6--><div class="ui text container" id="zettel-container" style="position: relative"><div class="zettel-view"><article class="ui raised attached segment zettel-content"><div class="pandoc"><h1 id="title-h1">Modules</h1><blockquote><p>Modules are partitioned files where we define our variables and functions. Values defined in modules are scoped to that specific module, constituting a unique name space. This avoids name clashes in large programs.</p></blockquote><ul><li><p>Every file in a Node application is considered a module.</p></li><li><p>The variables and methods in a module are equivalent to <code>private</code> properties and methods in object-oriented programming.</p></li><li><p>If you wish to use a function or variable defined in a module outside of its modular container you need to explicitly export it and make it public.</p></li></ul><h2 id="structure-of-a-module">Structure of a module</h2><p>Node keeps an internal record of the properties of a module. To see this we can log the property <code>module</code> to the console.</p><pre><code class="js language-js">// index.js
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console.log(module);</code></pre><p>This gives us:</p><pre><code class="plaintext language-plaintext">Module {
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id: '.',
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path: '/home/thomas/repos/node-learning',
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exports: {},
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filename: '/home/thomas/repos/node-learning/index.js',
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loaded: false,
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children: [],
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paths: [
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'/home/thomas/repos/node-learning/node_modules',
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'/home/thomas/repos/node_modules',
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'/home/thomas/node_modules',
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'/home/node_modules',
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'/node_modules'
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]
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}</code></pre><h2 id="exports">Exports</h2><ul><li>Whenever we export a property or method from a module we are directly targeting the <code>exports</code> property of the module object.</li><li>Once we add exports to a file they will be displayed under that property of the module object.</li><li>We can export the entire module itself as the export (typically used when the module is a single function or class) or individual properties.</li></ul><h3 id="exporting-a-whole-module">Exporting a whole module</h3><p><em>The example below is a module file that consists in a single function</em></p><pre><code class="js language-js">module.exports = function (...params) {
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// function body
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};</code></pre><p>Note the module is unnamed. We would name it when we import:</p><pre><code class="js language-js">const myFunction = require("./filenme");</code></pre><h3 id="exporting-sub-components-from-a-module">Exporting sub-components from a module</h3><p>In the example below we export a variable and function from the same module. Note only those values prefixed with <code>exports</code> are exported.</p><pre><code class="js language-js">exports.myFunc = (...params) => {
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// function bod[]()y
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};
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exports.aVar = 321.3;
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var nonExportedVar = true;</code></pre><p>This time the exports are already name so we would import with the following:</p><pre><code class="js language-js">const { myFunc, aVar } = require("./filename");</code></pre><p>We can also do the exporting at the bottom when the individual components are named:</p><pre><code class="js language-js">const myNamedFunc = (val) => {
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return val + 1;
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};
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function anotherNamedFunc(val) {
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return val * 2;
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}
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// This time we export at the bottom
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exports.myNamedFunc = myNamedFunc;
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exports.differentName = anotherNamedFunc; // We can use different names
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// Or we could export them together
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module.exports = { myNamedFunc, anotherNamedFunc };</code></pre><p>The import is the same:</p><pre><code class="js language-js">const { myNamedFunc, anotherNamedFunc } = require("./modules/multiExports");</code></pre><h2 id="structuring-modules">Structuring modules</h2><p>The techniques above are useful to know but generally you would want to enforce a stricter structure than a mix of exported and private values in the one file. The best way to do this is with a single default export.</p><p>Here the thing exported could be a composite function or an object that basically acts like a class with methods and properties.</p><p><em>Export a composite single function</em></p><pre><code class="js language-js">
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module.exports = () => {
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foo() {...}
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bar() {...}
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}</code></pre><p><em>Export an object</em></p><pre><code class="js language-js">
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module.exports = {
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foo : () => {...},
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bar: () => {...}
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}</code></pre><p><strong>Both of these structures would be referred to in the same way when importing and using them.</strong></p><p>Or you could export an actual class as the default. This is practically the same as the two above other than that you would have to use <code>new</code> to initiate an instance of the class.</p><pre><code class="js language-js">export default class {
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foo() {}
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bar() {}
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}</code></pre><p>Every method and property within the export will be public by default, whether it is an object, class or function. If you wanted to keep certain methods/properties private, the best approach is to define them as variables and functions within the module file but outside of the <code>export</code> block.</p></div></article><nav class="ui attached segment deemphasized bottomPane" id="neuron-tags-pane"><div><span class="ui basic label zettel-tag" title="Tag">node-js</span></div></nav><nav class="ui bottom attached icon compact inverted menu blue" id="neuron-nav-bar"><!--replace-start-9--><!--replace-end-9--><a class="right item" href="impulse.html" title="Open Impulse"><i class="wave square icon"></i></a></nav></div></div><!--replace-end-6--><!--replace-end-3--><!--replace-end-2--><div class="ui center aligned container footer-version"><div class="ui tiny image"><a href="https://neuron.zettel.page"><img alt="logo" src="https://raw.githubusercontent.com/srid/neuron/master/assets/neuron.svg" title="Generated by Neuron 1.9.35.3" /></a></div></div></div></body></html>
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