<!DOCTYPE html><html><head><metacharset="utf-8"><metaname="viewport"content="width=device-width, initial-scale=1"><metaname="description"content="Using not only events in UI declaratively."><title>`deka-dom-el` — Events and Addons</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` — Events and Addons</h1><p>Using not only events in UI declaratively.</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."class="current">3. Events and Addons</a><ahref="p04-observables"title="Handling reactivity in UI via observables.">4. Observables and reactivity</a><ahref="p05-scopes"title="Organizing UI into components">5. Scopes and components</a><ahref="p06-customElement"title="Using custom elements in combinantion with DDE">6. Custom elements</a></nav><main><h2>Listenning to the native DOM events and other Addons</h2><p>We quickly introduce helper to listening to the native DOM events. And library syntax/pattern so-called <em>Addon</em> to incorporate not only this in UI templates declaratively.</p><divclass="code"data-js="todo"><!--<dde:mark type="component" name="code" host="parentElement" ssr/>--><codeclass="language-js">// use NPM or for example https://cdn.jsdelivr.net/gh/jaandrle/deka-dom-el/dist/esm.js
</code></div><h3id="h-events-and-listenners"><!--<dde:mark type="component" name="h3" host="parentElement" ssr/>--><ahref="#h-events-and-listenners"tabindex="-1">#</a> Events and listenners</h3><p>In JavaScript you can listen to the native DOM events of the given element by using <ahref="https://developer.mozilla.org/en-US/docs/Web/API/EventTarget/addEventListener"title="addEventListener on MDN"><code>element.addEventListener(type, listener, options)</code></a>. The library provides an alternative (<code>on</code>) accepting the differen order of the arguments:</p><!--<dde:mark type="component" name="example" host="this" ssr/>--><divid="code-example-1-1wmddlo83w68"class="example"><!--<dde:mark type="component" name="code" host="parentElement" ssr/>--><codeclass="language-js">import { el, on } from "https://cdn.jsdelivr.net/gh/jaandrle/deka-dom-el/dist/esm-with-observables.js";
</code></div><script>Flems(document.getElementById("code-example-1-1wmddlo83w68"),JSON.parse("{\"files\":[{\"name\":\".js\",\"content\":\"import { el, on } from \\\"https://cdn.jsdelivr.net/gh/jaandrle/deka-dom-el/dist/esm-with-observables.js\\\";\\nconst log= mark=> console.log.bind(console, mark);\\n\\nconst button= el(\\\"button\\\", \\\"Test click\\\");\\nbutton.addEventListener(\\\"click\\\", log(\\\"`addEventListener`\\\"), { once: true });\\non(\\\"click\\\", log(\\\"`on`\\\"), { once: true })(button);\\n\\ndocument.body.append(\\n\\tbutton\\n);\\n\"}],\"toolbar\":false}"));</script><p>…this is actually one of the two differences. The another one is that <code>on</code> accepts only object as the <code>options</code> (but it is still optional).</p><pclass="notice">The other difference is that there is <strong>no</strong><code>off</code> function. You can remove listener declaratively using <ahref="https://developer.mozilla.org/en-US/docs/Web/API/EventTarget/addEventListener#signal"title="part of addEventListener on MDN">AbortSignal</a>:</p><!--<dde:mark type="component" name="example" host="this" ssr/>--><divid="code-example-1-8r8qappf8mo"class="example"><!--<dde:mark type="component" name="code" host="parentElement" ssr/>--><codeclass="language-js">import { el, on } from "https://cdn.jsdelivr.net/gh/jaandrle/deka-dom-el/dist/esm-with-observables.js";
</code></div><script>Flems(document.getElementById("code-example-1-8r8qappf8mo"),JSON.parse("{\"files\":[{\"name\":\".js\",\"content\":\"import { el, on } from \\\"https://cdn.jsdelivr.net/gh/jaandrle/deka-dom-el/dist/esm-with-observables.js\\\";\\nconst log= mark=> console.log.bind(console, mark);\\n\\nconst abort_controller= new AbortController();\\nconst { signal }= abort_controller;\\n\\nconst button= el(\\\"button\\\", \\\"Test click\\\");\\nbutton.addEventListener(\\\"click\\\", log(\\\"`addEventListener`\\\"), { signal });\\non(\\\"click\\\", log(\\\"`on`\\\"), { signal })(button);\\n\\ndocument.body.append(\\n\\tbutton, \\\" \\\", el(\\\"button\\\", { textContent: \\\"Off\\\", onclick: ()=> abort_controller.abort() })\\n);\\n\"}],\"toolbar\":false}"));</script><divclass="notice"><p>So, there are (typically) three ways to handle events. You can use:</p><ul><li><code>el("button", { textContent: "click me", "=onclick": "console.log(event)" })</code></li><li><code>el("button", { textContent: "click me", onclick: console.log })</code></li><li><code>el("button", { textContent: "click me" }, on("click", console.log))</code></li></ul><p>In the first example we force to use HTML attribute (it corresponds to <code><button onclick="console.log(event)">click me</button></code>). <em>Side note: this can be useful in case of SSR.</em> To study difference, you can read a nice summary here: <ahref="https://gist.github.com/WebReflection/b404c36f46371e3b1173bf5492acc944">GIST @WebReflection/web_events.md</a>.</p></div><h3id="h-addons"><!--<dde:mark type="component" name="h3" host="parentElement" ssr/>--><ahref="#h-addons"tabindex="-1">#</a> Addons</h3><p>From practical point of view, <em>Addons</em> are just functions that accept any html element as their first parameter. You can see that the <code>on(…)</code> fullfills this requirement.</p><p>You can use Addons as ≥3rd argument of <code>el</code> function. This way is possible to extends you templates by additional (3rd party) functionalities. But for now mainly, you can add events listeners:</p><!--<dde:mark type="component" name="example" host="this" ssr/>--><divid="code-example-1-6jtsnxfqzm4"class="example"><!--<dde:mark type="component" name="code" host="parentElement" ssr/>--><codeclass="language-js">import { el, on } from "https://cdn.jsdelivr.net/gh/jaandrle/deka-dom-el/dist/esm-with-observables.js";
</code></div><script>Flems(document.getElementById("code-example-1-6jtsnxfqzm4"),JSON.parse("{\"files\":[{\"name\":\".js\",\"content\":\"import { el, on } from \\\"https://cdn.jsdelivr.net/gh/jaandrle/deka-dom-el/dist/esm-with-observables.js\\\";\\nconst abort_controller= new AbortController();\\nconst { signal }= abort_controller;\\n/** @type {ddeElementAddon<HTMLButtonElement>} */\\nconst onclickOff= on(\\\"click\\\", ()=> abort_controller.abort(), { signal });\\n/** @type {(ref?: HTMLOutputElement)=> HTMLOutputElement | null} */\\nconst ref= (store=> ref=> ref ? (store= ref) : store)(null);\\n\\ndocument.body.append(\\n\\tel(\\\"button\\\", \\\"Test `on`\\\",\\n\\t\\ton(\\\"click\\\", console.log, { signal }),\\n\\t\\ton(\\\"click\\\", update, { signal }),\\n\\t\\ton(\\\"mouseup\\\", update, { signal })),\\n\\t\\\" \\\",\\n\\tel(\\\"button\\\", \\\"Off\\\", onclickOff),\\n\\tel(\\\"output\\\", { style: { display: \\\"block\\\", whiteSpace: \\\"pre\\\" } }, ref)\\n);\\n/** @param {MouseEvent} event @this {HTMLButtonElement} */\\nfunction update(event){\\n\\tref().append(\\n\\t\\tevent.type,\\n\\t\\t\\\"\\\\n\\\"\\n\\t);\\n}\\n\"}],\"toolbar\":false}"));</script><p>As the example shows, you can also provide types in JSDoc+TypeScript by using global type <code>ddeElementAddon</code>. Also notice, you can use Addons to get element reference.</p><h3id="h-life-cycle-events"><!--<dde:mark type="component" name="h3" host="parentElement" ssr/>--><ahref="#h-life-cycle-events"tabindex="-1">#</a> Life-cycle events</h3><p>Addons are called immediately when the element is created, even it is not connected to live DOM yet. Therefore, you can understand the Addon to be “oncreate” event.</p><p>The library provide three additional live-cycle events corresponding to how they are named in a case of custom elements: <code>on.connected</code>, <code>on.disconnected</code> and <code>on.attributeChanged</code>.</p><!--<dde:mark type="component" name="example" host="this" ssr/>--><divid="code-example-1-35hjjp3e4js"class="example"><!--<dde:mark type="component" name="code" host="parentElement" ssr/>--><codeclass="language-js">import { el, on } from "https://cdn.jsdelivr.net/gh/jaandrle/deka-dom-el/dist/esm-with-observables.js";
</code></div><script>Flems(document.getElementById("code-example-1-35hjjp3e4js"),JSON.parse("{\"files\":[{\"name\":\".js\",\"content\":\"import { el, on } from \\\"https://cdn.jsdelivr.net/gh/jaandrle/deka-dom-el/dist/esm-with-observables.js\\\";\\nconst paragraph= el(\\\"p\\\", \\\"See live-cycle events in console.\\\",\\n\\tel=> log({ type: \\\"dde:created\\\", detail: el }),\\n\\ton.connected(log),\\n\\ton.disconnected(log),\\n\\ton.attributeChanged(log));\\n\\ndocument.body.append(\\n\\tparagraph,\\n\\tel(\\\"button\\\", \\\"Update attribute\\\", on(\\\"click\\\", ()=> paragraph.setAttribute(\\\"test\\\", Math.random().toString()))),\\n\\t\\\" \\\",\\n\\tel(\\\"button\\\", \\\"Remove\\\", on(\\\"click\\\", ()=> paragraph.remove()))\\n);\\n\\n/** @param {Partial<CustomEvent>} event */\\nfunction log({ type, detail }){\\n\\tconsole.log({ _this: this, type, detail });\\n}\\n\"}],\"toolbar\":false}"));</script><p>For Custom elements, we will later introduce a way to replace <code>*Callback</code> syntax with <code>dde:*</code> events. The <code>on.*</code> functions then listen to the appropriate Custom Elements events (see <ahref="https://developer.mozilla.org/en-US/docs/Web/API/Web_components/Using_custom_elements#custom_element_lifecycle_callbacks">Custom element lifecycle callbacks | MDN</a>).</p><p>But, in case of regular elemnets the <ahref="https://developer.mozilla.org/en-US/docs/Web/API/MutationObserver"><code>MutationObserver</code> | MDN</a> is internaly used to track these events. Therefore, there are some drawbacks:</p><ul><li>To proper listener registration, you need to use <code>on.*</code> not `on("dde:*", …)`!</li><li>Use sparingly! Internally, library must loop of all registered events and fires event properly. <strong>It is good practice to use the fact that if an element is removed, its children are also removed!</strong> In this spirit, we will introduce later the <strong>host</strong> syntax to register clean up procedures when the component is removed from the app.</li></ul><p>To provide intuitive behaviour, similar also to how the life-cycle events works in other frameworks/libraries, deka-dom-el library ensures that <code>on.connected</code> and <code>on.disconnected</code> are called only once and only when the element is (dis)connected to live DOM. The solution is inspired by <ahref="https://vuejs.org/guide/extras/web-components.html#lifecycle"title="Vue and Web Components | Lifecycle">Vue</a>. For using native behaviour re-(dis)connecting element, use:</p><ul><li>custom <code>MutationObserver</code> or logic in (dis)<divclass="code"><!--<dde:mark type="component" name="code" host="parentElement" ssr/>--><codeclass="language-js"></code></div> or…</li><li>re-add <code>on.connected</code> or <code>on.disconnected</code> listeners.</li></ul><h3id="h-final-notes"><!--<dde:mark type="component" name="h3" host="parentElement" ssr/>--><ahref="#h-final-notes"tabindex="-1">#</a> Final notes</h3><p>The library also provides a method to dispatch the events.</p><!--<dde:mark type="component" name="example" host="this" ssr/>--><divid="code-example-2-b6a1hbrxh7s"class="example"><!--<dde:mark type="component" name="code" host="parentElement" ssr/>--><codeclass="language-js">import { el, on, dispatchEvent } from "https://cdn.jsdelivr.net/gh/jaandrle/deka-dom-el/dist/esm-with-observables.js";
