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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">Module pattern</h1><blockquote><p>Come back and compare this with learning from Node.js</p></blockquote><p>With the module design pattern we create encapsulation: the variables and functions (as methods) are kept private inside the module and cannot be overwritten. This design pattern is familiar from Node.js development: every package you import into your project and download from NPM is a module.</p><p>Generally you will create the module as a class, import it and then instantiate a new instance. However for private development, you could just as well use an object and duplicate it with <code>Object.create</code>.</p><h2 id="example">Example</h2><p>Here is an example of a simple module that returns the age of a person.</p><pre><code class="js language-js">export default class Age {
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constructor(name, birthYear) {
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this.name = name;
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this.birthYear = birthYear;
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}
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currentYear() {
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return new Date().getFullYear();
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}
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get age() {
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return this.currentYear() - this.birthYear;
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}
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}</code></pre><pre><code class="js language-js">const martha = new Age("Martha", 1997);
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console.log(martha.age); // 24</code></pre><h2 id="controlling-access">Controlling access</h2><p>In the example above, <code>aValue</code> could be edited in instantiations of the class. Given that modules should not be overwrittable, you could make it a private property on the class. The benefit of getters and setters is that they dictate what can be modified and retrieved from the module. So if you use <code>get</code> and <code>set</code> you can prevent overwrites.</p><h2 id="object-modules">Object modules</h2><p>If you want to use an object instead of a class, you have to take greater care to ensure that the objects are not overwritable. <strong>Also you cannot use the <code>#</code> modifier to make properties private.</strong></p><ul><li>Use getters and setters for updating and retrieving values</li><li>Use <code>Object.seal</code> to prevent changes to the parent object</li><li>Instead of using getters and setters, for individual properties you can set <code>writable</code> to be <code>false</code> for properties that you don’t want changed</li></ul><p>There are examples of each in the following:</p><pre><code class="jsx language-jsx">export const age = {
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name: "",
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birthYear: new Number(),
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currentYear() {
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return new Date().getFullYear();
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},
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get age() {
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return this.currentYear() - this.birthYear;
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},
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};
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Object.seal(age);
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Object.defineProperty(age, "aValue", {
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value: 6,
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writable: false,
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});</code></pre></div></article><nav class="ui attached segment deemphasized bottomPane" id="neuron-tags-pane"><div><span class="ui basic label zettel-tag" title="Tag">OOP</span><span class="ui basic label zettel-tag" title="Tag">design-patterns</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> |