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150 lines
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150 lines
22 KiB
HTML
<!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><a href="p05-scopes" title="Organizing UI into components">5. Scopes and components</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">// use NPM or for example https://cdn.jsdelivr.net/gh/jaandrle/deka-dom-el/dist/esm-with-observables.js
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import { O, observable } from "deka-dom-el/observables";
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O===observable
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/** @type {ddeObservable} */
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/** @type {ddeAction} */
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/** @type {ddeActions} */
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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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const update= ()=> observable(observable()+1);
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update();
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const interval= 5*1000;
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setTimeout(clearInterval, 10*interval,
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setInterval(update, interval));
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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\\nconst update= ()=> observable(observable()+1);\\n\\nupdate();\\nconst interval= 5*1000;\\nsetTimeout(clearInterval, 10*interval,\\n\\tsetInterval(update, interval));\\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. In example, you also found the way for representing “live” piece of code computation pattern (derived observable):</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= 5 * 1000;
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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= 5 * 1000;\\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><h3 id="h-observables-and-actions"><!--<dde:mark type="component" name="h3" host="parentElement" ssr/>--><a href="#h-observables-and-actions" tabindex="-1">#</a> Observables and actions</h3><p><code>O(/* primitive */)</code> allows you to declare simple reactive variables, typically around <em>immutable</em> <a title="Primitive | MDN" href="https://developer.mozilla.org/en-US/docs/Glossary/Primitive">primitive types</a>. However, it may also be necessary to use reactive arrays, objects, or other complex reactive structures.</p><!--<dde:mark type="component" name="example" host="this" ssr/>--><div id="code-example-1-ny81g2qun6o" 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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increaseOnlyOdd(add){
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console.info(add);
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if(add%2 === 0) return this.stopPropagation();
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this.value+= add;
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}
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});
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O.on(observable, console.log);
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const oninterval= ()=>
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O.action(observable, "increaseOnlyOdd", Math.floor(Math.random()*100));
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const interval= 5*1000;
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setTimeout(
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clearInterval,
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10*interval,
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setInterval(oninterval, interval)
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);
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</code></div><script>Flems(document.getElementById("code-example-1-ny81g2qun6o"), 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\\tincreaseOnlyOdd(add){\\n\\t\\tconsole.info(add);\\n\\t\\tif(add%2 === 0) return this.stopPropagation();\\n\\t\\tthis.value+= add;\\n\\t}\\n});\\nO.on(observable, console.log);\\nconst oninterval= ()=>\\n\\tO.action(observable, \\\"increaseOnlyOdd\\\", Math.floor(Math.random()*100));\\n\\nconst interval= 5*1000;\\nsetTimeout(\\n\\tclearInterval,\\n\\t10*interval,\\n\\tsetInterval(oninterval, interval)\\n);\\n\"}],\"toolbar\":false}"));</script><p>…but typical user-case is object/array (maps, sets and other mutable objects):</p><!--<dde:mark type="component" name="example" host="this" ssr/>--><div id="code-example-1-ihanc6k9v9c" 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 todos= O([], {
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push(item){
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this.value.push(O(item));
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},
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pop(){
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const removed= this.value.pop();
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if(removed) O.clear(removed);
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},
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[O.symbols.onclear](){ // this covers `O.clear(todos)`
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O.clear(...this.value);
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}
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});
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import { el, on } from "https://cdn.jsdelivr.net/gh/jaandrle/deka-dom-el/dist/esm-with-observables.js";
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/** @type {ddeElementAddon<HTMLFormElement>} */
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const onsubmit= on("submit", function(event){
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event.preventDefault();
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const data= new FormData(this);
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switch (data.get("op")){
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case "A"/*dd*/:
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O.action(todos, "push", data.get("todo"));
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break;
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case "E"/*dit*/: {
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const last= todos().at(-1);
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if(!last) break;
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last(data.get("todo"));
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break;
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}
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case "R"/*emove*/:
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O.action(todos, "pop");
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break;
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}
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});
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document.body.append(
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el("ul").append(
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O.el(todos, todos=>
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todos.map(textContent=> el("li", textContent)))
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),
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el("form", null, onsubmit).append(
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el("input", { type: "text", name: "todo", placeholder: "Todo’s text" }),
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el(radio, { textContent: "Add", checked: true }),
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el(radio, { textContent: "Edit last" }),
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el(radio, { textContent: "Remove" }),
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el("button", "Submit")
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)
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);
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document.head.append(
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el("style", "form{ display: flex; flex-flow: column nowrap; }")
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);
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function radio({ textContent, checked= false }){
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return el("label").append(
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el("input", { type: "radio", name: "op", value: textContent[0], checked }),
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" ",textContent
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)
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}
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</code></div><script>Flems(document.getElementById("code-example-1-ihanc6k9v9c"), JSON.parse("{\"files\":[{\"name\":\".js\",\"content\":\"import { O } from \\\"https://cdn.jsdelivr.net/gh/jaandrle/deka-dom-el/dist/esm-with-observables.js\\\";\\nconst todos= O([], {\\n\\tpush(item){\\n\\t\\tthis.value.push(O(item));\\n\\t},\\n\\tpop(){\\n\\t\\tconst removed= this.value.pop();\\n\\t\\tif(removed) O.clear(removed);\\n\\t},\\n\\t[O.symbols.onclear](){ // this covers `O.clear(todos)`\\n\\t\\tO.clear(...this.value);\\n\\t}\\n});\\n\\nimport { el, on } from \\\"https://cdn.jsdelivr.net/gh/jaandrle/deka-dom-el/dist/esm-with-observables.js\\\";\\n/** @type {ddeElementAddon<HTMLFormElement>} */\\nconst onsubmit= on(\\\"submit\\\", function(event){\\n\\tevent.preventDefault();\\n\\tconst data= new FormData(this);\\n\\tswitch (data.get(\\\"op\\\")){\\n\\t\\tcase \\\"A\\\"/*dd*/:\\n\\t\\t\\tO.action(todos, \\\"push\\\", data.get(\\\"todo\\\"));\\n\\t\\t\\tbreak;\\n\\t\\tcase \\\"E\\\"/*dit*/: {\\n\\t\\t\\tconst last= todos().at(-1);\\n\\t\\t\\tif(!last) break;\\n\\t\\t\\tlast(data.get(\\\"todo\\\"));\\n\\t\\t\\tbreak;\\n\\t\\t}\\n\\t\\tcase \\\"R\\\"/*emove*/:\\n\\t\\t\\tO.action(todos, \\\"pop\\\");\\n\\t\\t\\tbreak;\\n\\t}\\n});\\ndocument.body.append(\\n\\tel(\\\"ul\\\").append(\\n\\t\\tO.el(todos, todos=>\\n\\t\\t\\ttodos.map(textContent=> el(\\\"li\\\", textContent)))\\n\\t),\\n\\tel(\\\"form\\\", null, onsubmit).append(\\n\\t\\tel(\\\"input\\\", { type: \\\"text\\\", name: \\\"todo\\\", placeholder: \\\"Todo’s text\\\" }),\\n\\t\\tel(radio, { textContent: \\\"Add\\\", checked: true }),\\n\\t\\tel(radio, { textContent: \\\"Edit last\\\" }),\\n\\t\\tel(radio, { textContent: \\\"Remove\\\" }),\\n\\t\\tel(\\\"button\\\", \\\"Submit\\\")\\n\\t)\\n);\\ndocument.head.append(\\n\\tel(\\\"style\\\", \\\"form{ display: flex; flex-flow: column nowrap; }\\\")\\n);\\nfunction radio({ textContent, checked= false }){\\n\\treturn el(\\\"label\\\").append(\\n\\t\\tel(\\\"input\\\", { type: \\\"radio\\\", name: \\\"op\\\", value: textContent[0], checked }),\\n\\t\\t\\\" \\\",textContent\\n\\t)\\n}\\n\"}],\"toolbar\":false}"));</script><p>In some way, you can compare it with <a href="https://react.dev/reference/react/useReducer" title="useReducer hook | React docs">useReducer</a> hook from React. So, the <code>O(<data>, <actions>)</code> pattern creates a store “machine”. We can then invoke (dispatch) registered action by calling <code>O.action(<observable>, <name>, ...<args>)</code> after the action call the observable calls all its listeners. This can be stopped by calling <code>this.stopPropagation()</code> in the method representing the given action. As it can be seen in examples, the “store” value is available also in the function for given action (<code>this.value</code>).</p><h3 id="h-reactive-dom-attributes-and-elements"><!--<dde:mark type="component" name="h3" host="parentElement" ssr/>--><a href="#h-reactive-dom-attributes-and-elements" tabindex="-1">#</a> Reactive DOM attributes and elements</h3><p>There are on basic level two distinc situation to mirror dynamic value into the DOM/UI</p><ol><li>to change some attribute(s) of existing element(s)</li><li>to generate elements itself dynamically – this covers conditions and loops</li></ol><!--<dde:mark type="component" name="example" host="this" ssr/>--><div id="code-example-1-ehcq40v0h5k" 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 count= O(0);
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import { el } from "https://cdn.jsdelivr.net/gh/jaandrle/deka-dom-el/dist/esm-with-observables.js";
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document.body.append(
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el("p", O(()=> "Currently: "+count())),
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el("p", { classList: { red: O(()=> count()%2) }, dataset: { count }, textContent: "Attributes example" })
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);
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document.head.append(
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el("style", ".red { color: red; }")
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);
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const interval= 5 * 1000;
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setTimeout(clearInterval, 10*interval,
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setInterval(()=> count(count()+1), interval));
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</code></div><script>Flems(document.getElementById("code-example-1-ehcq40v0h5k"), JSON.parse("{\"files\":[{\"name\":\".js\",\"content\":\"import { O } from \\\"https://cdn.jsdelivr.net/gh/jaandrle/deka-dom-el/dist/esm-with-observables.js\\\";\\nconst count= O(0);\\n\\nimport { el } from \\\"https://cdn.jsdelivr.net/gh/jaandrle/deka-dom-el/dist/esm-with-observables.js\\\";\\ndocument.body.append(\\n\\tel(\\\"p\\\", O(()=> \\\"Currently: \\\"+count())),\\n\\tel(\\\"p\\\", { classList: { red: O(()=> count()%2) }, dataset: { count }, textContent: \\\"Attributes example\\\" })\\n);\\ndocument.head.append(\\n\\tel(\\\"style\\\", \\\".red { color: red; }\\\")\\n);\\n\\nconst interval= 5 * 1000;\\nsetTimeout(clearInterval, 10*interval,\\n\\tsetInterval(()=> count(count()+1), interval));\\n\"}],\"toolbar\":false}"));</script><p>To derived attribute based on value of observable variable just use the observable as a value of the attribute (<code>assign(element, { attribute: O('value') })</code>). <code>assign</code>/<code>el</code> provides ways to glue reactive attributes/classes more granularly into the DOM. Just use dedicated build-in attributes <code>dataset</code>, <code>ariaset</code> and <code>classList</code>.</p><p>For computation, you can use the “derived observable” (see above) like <code>assign(element, { textContent: O(()=> 'Hello '+WorldObservable()) })</code>. This is read-only observable its value is computed based on given function and updated when any observable used in the function changes.</p><p>To represent part of the template filled dynamically based on the observable value use <code>O.el(observable, DOMgenerator)</code>. This was already used in the todo example above or see:</p><!--<dde:mark type="component" name="example" host="this" ssr/>--><div id="code-example-2-8r8qappf8mo" 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 count= O(0, {
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add(){ this.value= this.value + Math.round(Math.random()*10); }
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});
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const numbers= O([ count() ], {
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push(next){ this.value.push(next); }
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});
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import { el } from "https://cdn.jsdelivr.net/gh/jaandrle/deka-dom-el/dist/esm-with-observables.js";
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document.body.append(
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O.el(count, count=> count%2
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? el("p", "Last number is odd.")
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: el()
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),
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el("p", "Lucky numbers:"),
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el("ul").append(
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O.el(numbers, numbers=> numbers.toReversed()
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.map(n=> el("li", n)))
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)
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);
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const interval= 5*1000;
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setTimeout(clearInterval, 10*interval, setInterval(function(){
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O.action(count, "add");
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O.action(numbers, "push", count());
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}, interval));
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</code></div><script>Flems(document.getElementById("code-example-2-8r8qappf8mo"), JSON.parse("{\"files\":[{\"name\":\".js\",\"content\":\"import { O } from \\\"https://cdn.jsdelivr.net/gh/jaandrle/deka-dom-el/dist/esm-with-observables.js\\\";\\nconst count= O(0, {\\n\\tadd(){ this.value= this.value + Math.round(Math.random()*10); }\\n});\\nconst numbers= O([ count() ], {\\n\\tpush(next){ this.value.push(next); }\\n});\\n\\nimport { el } from \\\"https://cdn.jsdelivr.net/gh/jaandrle/deka-dom-el/dist/esm-with-observables.js\\\";\\ndocument.body.append(\\n\\tO.el(count, count=> count%2\\n\\t\\t? el(\\\"p\\\", \\\"Last number is odd.\\\")\\n\\t\\t: el()\\n\\t),\\n\\tel(\\\"p\\\", \\\"Lucky numbers:\\\"),\\n\\tel(\\\"ul\\\").append(\\n\\t\\tO.el(numbers, numbers=> numbers.toReversed()\\n\\t\\t\\t.map(n=> el(\\\"li\\\", n)))\\n\\t)\\n);\\n\\nconst interval= 5*1000;\\nsetTimeout(clearInterval, 10*interval, setInterval(function(){\\n\\tO.action(count, \\\"add\\\");\\n\\tO.action(numbers, \\\"push\\\", count());\\n}, interval));\\n\"}],\"toolbar\":false}"));</script><div class="notice"><!--<dde:mark type="component" name="mnemonic" 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> — read-only 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><li><code>O.el(<observable>, <function-returning-dom>)</code> — render partial dom structure (template) based on the current observable value</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><a rel="next" href="p05-scopes" title="Organizing UI into components"><!--<dde:mark type="component" name="pageLink" host="parentElement" ssr/>-->(next) Scopes and components</a></div></main></body></html> |