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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"><code>http</code> module</h1><p>The HTTP Module allows us to create a web server that listens for HTTP requests on a given port. It is therefore perfect for creating backends for client-side JavaScript.</p><h2 id="creating-a-server">Creating a server</h2><p>An HTTP server is another instance of an <span class="zettel-link-container errors"><span class="zettel-link" title="Wiki-link does not refer to any existing zettel"><a>events</a></span></span>). It therefore has all the same methods as the <code>EventEmitter</code> class: <code>on</code>, <code>emit</code>, <code>addListener</code> etc. This demonstrates again how much of Node’s core functionality is based on event emitters.</p><p><em>Creating a server</em></p><pre><code class="js language-js">const http = require("http");
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const server = http.createServer(); // Create server as emitter
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// Register functions to run when listener is triggered
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server.on("connection", (socket) => {
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console.log("new connection...");
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});
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server.listen(3000);
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console.log("Listening on port 3000");</code></pre><p>This server is functionally equivalent to a generic event emitter:</p><pre><code class="js language-js">// Raise an event
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const emitter = new EventEmitter("messageLogged");
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// Register a listener
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emitter.on("messagedLogged", function () {
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console.log("The listener was called.");
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});</code></pre><p>Whenever a request is made to this server, it raises an event. We can therefore target it with the <code>on</code> method and make it execute a function when requests are made.</p><p>If we were to start the server by running the file and we then used a browser to navigate to the port, we would see <code>new connection</code> logged every time we refresh the page.</p><h3 id="sockets-and-req-res">Sockets and <code>req, res</code></h3><p>A socket is a generic protocol for client-server communication. Crucially it <strong>allows simultaneous communication both ways</strong>. The client can contact the server but the server can also contact the client. Our listener function above uses a socket as the callback function but in most cases this is quite low-level, not distinguishing responses from requests. It is more likely that you would initiate a <code>request, resource</code> architecture in place of a socket:</p><pre><code class="js language-js">const server = http.createServer((req, res) => {
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if (req.url === "/") {
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res.write("hello");
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res.end();
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}
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});</code></pre><h4 id="return-json">Return JSON</h4><p>Below is an example of using this architecture to return JSON to the client:</p><pre><code class="js language-js">const server = http.createServer((req, res) => {
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if (req.url === "/products") {
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res.write(JSON.stringify(["shoes", "lipstick", "cups"]));
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res.end();
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}
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});</code></pre><h3 id="express">Express</h3><p>In reality you would rarely use the <code>http</code> module directly to create a server. This is because it is quite low level and each response must be written in a linear fashion as with the two URLs in the previous example. Instead we use Express which is a framework for creating servers and routing that is an abstraction on top of the core HTTP module.</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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