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35 lines
9.6 KiB
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<!DOCTYPE html><html><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1"><meta name="description" content="Handling reactivity in UI via observables."><title>`deka-dom-el` — Observables and reactivity</title><!--<dde:mark type="component" name="metaAuthor" host="this" ssr/>--><meta name="author" content="Jan Andrle"><link type="text/plain" rel="author" href="https://jaandrle.github.io/humans.txt"><meta name="generator" content="deka-dom-el"><!--<dde:mark type="component" name="metaTwitter" host="this" ssr/>--><meta name="twitter:card" content="summary_large_image"><meta name="twitter:url" content="https://github.com/jaandrle/deka-dom-el"><meta name="twitter:title" content="deka-dom-el"><meta name="twitter:description" content="A low-code library that simplifies the creation of native DOM elements/components using small wrappers and tweaks."><meta name="twitter:creator" content="@jaandrle"><!--<dde:mark type="component" name="metaFacebook" host="this" ssr/>--><meta name="og:url" content="https://github.com/jaandrle/deka-dom-el"><meta name="og:title" content="deka-dom-el"><meta name="og:description" content="A low-code library that simplifies the creation of native DOM elements/components using small wrappers and tweaks."><meta name="og:creator" content="@jaandrle"><script src="https://cdn.jsdelivr.net/npm/shiki" defer=""></script><script type="module" src="code.js.js"></script><script src="https://flems.io/flems.html" type="text/javascript" charset="utf-8"></script><link rel="stylesheet" href="global.css"></head><body><!--<dde:mark type="component" name="page" host="this" ssr/>--><!--<dde:mark type="component" name="simplePage" host="this" ssr/>--><!--<dde:mark type="component" name="header" host="this" ssr/>--><header><h1>`deka-dom-el` — Observables and reactivity</h1><p>Handling reactivity in UI via observables.</p></header><nav><a href="https://github.com/jaandrle/deka-dom-el"><svg class="icon" viewBox="0 0 32 32"><!--<dde:mark type="component" name="iconGitHub" host="parentElement" ssr/>--><path d="M 16,0.395c -8.836,0 -16,7.163 -16,16c 0,7.069 4.585,13.067 10.942,15.182c 0.8,0.148 1.094,-0.347 1.094,-0.77c 0,-0.381 -0.015,-1.642 -0.022,-2.979c -4.452,0.968 -5.391,-1.888 -5.391,-1.888c -0.728,-1.849 -1.776,-2.341 -1.776,-2.341c -1.452,-0.993 0.11,-0.973 0.11,-0.973c 1.606,0.113 2.452,1.649 2.452,1.649c 1.427,2.446 3.743,1.739 4.656,1.33c 0.143,-1.034 0.558,-1.74 1.016,-2.14c -3.554,-0.404 -7.29,-1.777 -7.29,-7.907c 0,-1.747 0.625,-3.174 1.649,-4.295c -0.166,-0.403 -0.714,-2.03 0.155,-4.234c 0,0 1.344,-0.43 4.401,1.64c 1.276,-0.355 2.645,-0.532 4.005,-0.539c 1.359,0.006 2.729,0.184 4.008,0.539c 3.054,-2.07 4.395,-1.64 4.395,-1.64c 0.871,2.204 0.323,3.831 0.157,4.234c 1.026,1.12 1.647,2.548 1.647,4.295c 0,6.145 -3.743,7.498 -7.306,7.895c 0.574,0.497 1.085,1.47 1.085,2.963c 0,2.141 -0.019,3.864 -0.019,4.391c 0,0.426 0.288,0.925 1.099,0.768c 6.354,-2.118 10.933,-8.113 10.933,-15.18c 0,-8.837 -7.164,-16 -16,-16Z"></path></svg>GitHub</a><a href="./" title="Introducing a library.">1. Introduction</a><a href="p02-elements" title="Basic concepts of elements modifications and creations.">2. Elements</a><a href="p03-events" title="Using not only events in UI declaratively.">3. Events and Addons</a><a href="p04-observables" title="Handling reactivity in UI via observables." class="current">4. Observables and reactivity</a></nav><main><h2>Using observables to manage reactivity</h2><p>How a program responds to variable data or user interactions is one of the fundamental problems of programming. If we desire to solve the issue in a declarative manner, observables may be a viable approach.</p><div class="code" data-js="todo"><!--<dde:mark type="component" name="code" host="parentElement" ssr/>--><code class="language-js">// when NPM
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import { O } from "deka-dom-el/observables";
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// https://cdn.jsdelivr.net/gh/jaandrle/deka-dom-el/dist/esm-with-observables.js
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/**
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* @type {ddeObservable}
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* */
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/**
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* @type {ddeActions}
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* */
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</code></div><h3 id="h-introducing-observables"><!--<dde:mark type="component" name="h3" host="parentElement" ssr/>--><a href="#h-introducing-observables" tabindex="-1">#</a> Introducing observables</h3><p>Using observables, we split program logic into the three parts. Firstly (α), we create a variable (constant) representing reactive value. Somewhere later, we can register (β) a logic reacting to the observable value changes. Similarly, in a remaining part (γ), we can update the observable value.</p><!--<dde:mark type="component" name="example" host="this" ssr/>--><div id="code-example-1-v1fw44pkzuo" class="example"><!--<dde:mark type="component" name="code" host="parentElement" ssr/>--><code class="language-js">import { O } from "https://cdn.jsdelivr.net/gh/jaandrle/deka-dom-el/dist/esm-with-observables.js";
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// α — `observable` represents a reactive value
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const observable= O(0);
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// β — just reacts on observable changes
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O.on(observable, console.log);
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// γ — just updates the value
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observable(observable()+1);
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setInterval(()=> observable(observable()+1), 5000);
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</code></div><script>Flems(document.getElementById("code-example-1-v1fw44pkzuo"), JSON.parse("{\"files\":[{\"name\":\".js\",\"content\":\"import { O } from \\\"https://cdn.jsdelivr.net/gh/jaandrle/deka-dom-el/dist/esm-with-observables.js\\\";\\n// α — `observable` represents a reactive value\\nconst observable= O(0);\\n// β — just reacts on observable changes\\nO.on(observable, console.log);\\n// γ — just updates the value\\nobservable(observable()+1);\\nsetInterval(()=> observable(observable()+1), 5000);\\n\"}],\"toolbar\":false}"));</script><p>All this is just an example of <a href="https://en.wikipedia.org/wiki/Event-driven_programming" title="Wikipedia: Event-driven programming">Event-driven programming</a> and <a href="https://en.wikipedia.org/wiki/Publish%E2%80%93subscribe_pattern" title="Wikipedia: Publish–subscribe pattern">Publish–subscribe pattern</a> (compare for example with <a href="https://www.npmjs.com/package/fpubsub" title="NPM package: fpubsub">fpubsub library</a>). All three parts can be in some manner independent and still connected to the same reactive entity.</p><p>Observables are implemented in the library as functions. To see current value of observable, just call it without any arguments <code>console.log(observable())</code>. To update the observable value, pass any argument <code>observable('a new value')</code>. For listenning the observable value changes, use <code>O.on(observable, console.log)</code>.</p><p>Similarly to the <code>on</code> function to register DOM events listener. You can use <code>AbortController</code>/<code>AbortSignal</code> to <em>off</em>/stop listenning. For representing “live” piece of code computation pattern:</p><!--<dde:mark type="component" name="example" host="this" ssr/>--><div id="code-example-1-1ti9ynadhw5c" class="example"><!--<dde:mark type="component" name="code" host="parentElement" ssr/>--><code class="language-js">import { O } from "https://cdn.jsdelivr.net/gh/jaandrle/deka-dom-el/dist/esm-with-observables.js";
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const observable= O(0);
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// computation pattern
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const double= O(()=> 2*observable());
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const ac= new AbortController();
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O.on(observable, v=> console.log("observable", v), { signal: ac.signal });
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O.on(double, v=> console.log("double", v), { signal: ac.signal });
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observable(observable()+1);
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const interval= 5000;
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const id= setInterval(()=> observable(observable()+1), interval);
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ac.signal.addEventListener("abort",
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()=> setTimeout(()=> clearInterval(id), 2*interval));
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setTimeout(()=> ac.abort(), 3*interval)
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</code></div><script>Flems(document.getElementById("code-example-1-1ti9ynadhw5c"), JSON.parse("{\"files\":[{\"name\":\".js\",\"content\":\"import { O } from \\\"https://cdn.jsdelivr.net/gh/jaandrle/deka-dom-el/dist/esm-with-observables.js\\\";\\nconst observable= O(0);\\n// computation pattern\\nconst double= O(()=> 2*observable());\\n\\nconst ac= new AbortController();\\nO.on(observable, v=> console.log(\\\"observable\\\", v), { signal: ac.signal });\\nO.on(double, v=> console.log(\\\"double\\\", v), { signal: ac.signal });\\n\\nobservable(observable()+1);\\nconst interval= 5000;\\nconst id= setInterval(()=> observable(observable()+1), interval);\\nac.signal.addEventListener(\\\"abort\\\",\\n\\t()=> setTimeout(()=> clearInterval(id), 2*interval));\\n\\nsetTimeout(()=> ac.abort(), 3*interval)\\n\"}],\"toolbar\":false}"));</script><div class="notice"><!--<dde:mark type="component" name="mnemonicUl" host="parentElement" ssr/>--><h3 id="h-mnemonic"><!--<dde:mark type="component" name="h3" host="parentElement" ssr/>--><a href="#h-mnemonic" tabindex="-1">#</a> Mnemonic</h3><ul><li><code>O(<value>)</code> — observable: reactive value</li><li><code>O(()=> <computation>)</code> — observable: reactive value dependent on calculation using other observables</li><li><code>O.on(<observable>, <listener>[, <options>])</code> — listen to the observable value changes</li><li><code>O.clear(...<observables>)</code> — off and clear observables</li><li><code>O(<value>, <actions>)</code> — observable: pattern to create complex reactive objects/arrays</li><li><code>O.action(<observable>, <action-name>, ...<action-arguments>)</code> — invoke an action for given observable</li></ul></div><div class="prevNext"><!--<dde:mark type="component" name="prevNext" host="parentElement" ssr/>--><a rel="prev" href="p03-events" title="Using not only events in UI declaratively."><!--<dde:mark type="component" name="pageLink" host="parentElement" ssr/>-->Events and Addons (previous)</a><!--<dde:mark type="component" name="pageLink" host="this" ssr/>--></div></main></body></html>
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