<!DOCTYPE html><html><head><metacharset="utf-8"><metaname="viewport"content="width=device-width, initial-scale=1"><metaname="description"content="Handling reactivity in UI via signals."><title>`deka-dom-el` — Signals and reactivity</title><!--<dde:mark type="component" name="metaAuthor" host="this" ssr/>--><metaname="author"content="Jan Andrle"><linktype="text/plain"rel="author"href="https://jaandrle.github.io/humans.txt"><metaname="generator"content="deka-dom-el"><!--<dde:mark type="component" name="metaTwitter" host="this" ssr/>--><metaname="twitter:card"content="summary_large_image"><metaname="twitter:url"content="https://github.com/jaandrle/deka-dom-el"><metaname="twitter:title"content="deka-dom-el"><metaname="twitter:description"content="A low-code library that simplifies the creation of native DOM elements/components using small wrappers and tweaks."><metaname="twitter:creator"content="@jaandrle"><!--<dde:mark type="component" name="metaFacebook" host="this" ssr/>--><metaname="og:url"content="https://github.com/jaandrle/deka-dom-el"><metaname="og:title"content="deka-dom-el"><metaname="og:description"content="A low-code library that simplifies the creation of native DOM elements/components using small wrappers and tweaks."><metaname="og:creator"content="@jaandrle"><scriptsrc="https://cdn.jsdelivr.net/npm/shiki"defer=""></script><scripttype="module"src="code.js.js"></script><scriptsrc="https://flems.io/flems.html"type="text/javascript"charset="utf-8"></script><linkrel="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` — Signals and reactivity</h1><p>Handling reactivity in UI via signals.</p></header><nav><ahref="https://github.com/jaandrle/deka-dom-el"><svgclass="icon"viewBox="0 0 32 32"><!--<dde:mark type="component" name="iconGitHub" host="parentElement" ssr/>--><pathd="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><ahref="./"title="Introducing a library.">1. Introduction</a><ahref="p02-elements"title="Basic concepts of elements modifications and creations.">2. Elements</a><ahref="p03-events"title="Using not only events in UI declaratively.">3. Events and Addons</a><ahref="p04-signals"title="Handling reactivity in UI via signals."class="current">4. Signals and reactivity</a></nav><main><h2>Using signals 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, signals may be a viable approach.</p><divclass="code"data-js="todo"><!--<dde:mark type="component" name="code" host="parentElement" ssr/>--><codeclass="language-js">// when NPM
</code></div><h3id="h-introducing-signals"><!--<dde:mark type="component" name="h3" host="parentElement" ssr/>--><ahref="#h-introducing-signals"tabindex="-1">#</a> Introducing signals</h3><p>Using signals, 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 signal value changes. Similarly, in a remaining part (γ), we can update the signal value.</p><!--<dde:mark type="component" name="example" host="this" ssr/>--><divid="code-example-1-1gy5flu0x85c"class="example"><!--<dde:mark type="component" name="code" host="parentElement" ssr/>--><codeclass="language-js">import { S } from "https://cdn.jsdelivr.net/gh/jaandrle/deka-dom-el/dist/esm-with-signals.js";
</code></div><script>Flems(document.getElementById("code-example-1-1gy5flu0x85c"),JSON.parse("{\"files\":[{\"name\":\".js\",\"content\":\"import { S } from \\\"https://cdn.jsdelivr.net/gh/jaandrle/deka-dom-el/dist/esm-with-signals.js\\\";\\n// α — `signal` represents areactive value\\nconst signal= S(0);\\n// β — just reacts on signal changes\\nS.on(signal, console.log);\\n// γ — just updates the value\\nsignal(signal()+1);\\nsetInterval(()=> signal(signal()+1), 5000);\\n\"}],\"toolbar\":false}"));</script><p>All this is just an example of <ahref="https://en.wikipedia.org/wiki/Event-driven_programming"title="Wikipedia: Event-driven programming">Event-driven programming</a> and <ahref="https://en.wikipedia.org/wiki/Publish%E2%80%93subscribe_pattern"title="Wikipedia: Publish–subscribe pattern">Publish–subscribe pattern</a> (compare for example with <ahref="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>Signals are implemented in the library as functions. To see current value of signal, just call it without any arguments <code>console.log(signal())</code>. To update the signal value, pass any argument <code>signal('a new value')</code>. For listenning the signal value changes, use <code>S.on(signal, 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/>--><divid="code-example-1-e9cfsaeb64o"class="example"><!--<dde:mark type="component" name="code" host="parentElement" ssr/>--><codeclass="language-js">import { S } from "https://cdn.jsdelivr.net/gh/jaandrle/deka-dom-el/dist/esm-with-signals.js";
