<!DOCTYPE html><html><head><metacharset="utf-8"><metaname="viewport"content="width=device-width, initial-scale=1"><metaname="description"content="Organizing UI into components"><title>`deka-dom-el` — Scopes and components</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` — Scopes and components</h1><p>Organizing UI into components</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-observables"title="Handling reactivity in UI via observables.">4. Observables and reactivity</a><ahref="p05-scopes"title="Organizing UI into components"class="current">5. Scopes and components</a><ahref="p06-customElement"title="Using custom elements in combinantion with DDE">6. Custom elements</a></nav><main><h2>Using functions as UI components</h2><p>For state-less components we can use functions as UI components (see “Elements” page). But in real life, we may need to handle the component live-cycle and provide JavaScript the way to properly use the <ahref="https://developer.mozilla.org/en-US/docs/Glossary/Garbage_collection"title="Garbage collection | MDN">Garbage collection</a>.</p><divclass="code"data-js="todo"><!--<dde:mark type="component" name="code" host="parentElement" ssr/>--><cod
</code></div><p>The library therefore use <em>scopes</em> to provide these functionalities.</p><h3id="h-scopes-and-hosts"><!--<dde:mark type="component" name="h3" host="parentElement" ssr/>--><ahref="#h-scopes-and-hosts"tabindex="-1">#</a> Scopes and hosts</h3><p>The <strong>host</strong> is the name for the element representing the component. This is typically element returned by function. To get reference, you can use <code>scope.host()</code> to applly addons just use <code>scope.host(...<addons>)</code>.</p><!--<dde:mark type="component" name="example" host="this" ssr/>--><divid="code-example-1-8meex5b3tyo"class="example"><!--<dde:mark type="component" name="code" host="parentElement" ssr/>--><codeclass="language-js">import { el, on, scope } from "https://cdn.jsdelivr.net/gh/jaandrle/deka-dom-el/dist/esm-with-observables.js";
const { host }= scope;
host(
element=> console.log(
"This represents Addon/oninit for root",
element.outerHTML
)
);
console.log(
"This represents the reference to the host element of root",
host().outerHTML
);
document.body.append(
el(component)
);
function component(){
const { host }= scope;
host(
element=> console.log(
"This represents Addon/oninit for the component",
element.outerHTML
)
);
const onclick= on("click", function(ev){
console.log(
"This represents the reference to the host element of the component",
</code></div><script>Flems(document.getElementById("code-example-1-8meex5b3tyo"),JSON.parse("{\"files\":[{\"name\":\".js\",\"content\":\"import { el, on, scope } from \\\"https://cdn.jsdelivr.net/gh/jaandrle/deka-dom-el/dist/esm-with-observables.js\\\";\\nconst { host }= scope;\\nhost(\\n\\telement=> console.log(\\n\\t\\t\\\"This represents Addon/oninit for root\\\",\\n\\t\\telement.outerHTML\\n\\t)\\n);\\nconsole.log(\\n\\t\\\"This represents the reference to the host element of root\\\",\\n\\thost().outerHTML\\n);\\ndocument.body.append(\\n\\tel(component)\\n);\\nfunction component(){\\n\\tconst { host }= scope;\\n\\thost(\\n\\t\\telement=> console.log(\\n\\t\\t\\t\\\"This represents Addon/oninit for the component\\\",\\n\\t\\t\\telement.outerHTML\\n\\t\\t)\\n\\t);\\n\\tconst onclick= on(\\\"click\\\", function(ev){\\n\\t\\tconsole.log(\\n\\t\\t\\t\\\"This represents the reference to the host element of the component\\\",\\n\\t\\t\\thost().outerHTML\\n\\t\\t);\\n\\t})\\n\\treturn el(\\\"div\\\", null, onclick).append(\\n\\t\\tel(\\\"strong\\\", \\\"Component\\\")\\n\\t);\\n}\\n\"}],\"toolbar\":false}"));</script><p>To better understanding we implement function <code>elClass</code> helping to create component as class instances.</p><!--<dde:mark type="component" name="example" host="this" ssr/>--><divid="code-example-3-b6a1hbrxh7s"class="example"><!--<dde:mark type="component" name="code" host="parentElement" ssr/>--><codeclass="language-js">import { el } from "https://cdn.jsdelivr.net/gh/jaandrle/deka-dom-el/dist/esm-with-observables.js";
</code></div><script>Flems(document.getElementById("code-example-3-b6a1hbrxh7s"),JSON.parse("{\"files\":[{\"name\":\".js\",\"content\":\"import { el } from \\\"https://cdn.jsdelivr.net/gh/jaandrle/deka-dom-el/dist/esm-with-observables.js\\\";\\nclass Test {\\n\\tconstructor(params){\\n\\t\\tthis._params= params;\\n\\t}\\n\\trender(){\\n\\t\\treturn el(\\\"div\\\").append(\\n\\t\\t\\tthis._params.textContent\\n\\t\\t);\\n\\t}\\n}\\ndocument.body.append(\\n\\telClass(Test, { textContent: \\\"Hello World\\\" })\\n);\\n\\nimport { chainableAppend, scope } from \\\"https://cdn.jsdelivr.net/gh/jaandrle/deka-dom-el/dist/esm-with-observables.js\\\";\\nfunction elClass(_class, attributes, ...addons){\\n\\tlet element, element_host;\\n\\tscope.push({\\n\\t\\tscope: _class, //just informative purposes\\n\\t\\thost: (...addons_append)=> addons_append.length\\n\\t\\t\\t? (\\n\\t\\t\\t\\t!element\\n\\t\\t\\t\\t? addons.unshift(...addons_append)\\n\\t\\t\\t\\t: addons_append.forEach(c=> c(element_host))\\n\\t\\t\\t, undefined)\\n\\t\\t\\t: element_host\\n\\t});\\n\\tconst instance= new _class(attributes);\\n\\telement= instance.render();\\n\\tconst is_fragment= element instanceof DocumentFragment;\\n\\tconst el_mark= el.mark({ //this creates html comment `<dde:mark …/>`\\n\\t\\ttype: \\\"class-component\\\",\\n\\t\\tname: _class.name,\\n\\t\\thost: is_fragment ? \\\"this\\\" : \\\"parentElement\\\",\\n\\t});\\n\\telement.prepend(el_mark);\\n\\tif(is_fragment) element_host= el_mark;\\n\\t\\n\\tchainableAppend(element);\\n\\taddons.forEach(c=> c(element_host));\\n\\tscope.pop();\\n\\treturn element;\\n}\\n\"}],\"toolbar\":false}"));</script><p>As you can see, the <code>scope.host()</code> is stored temporarily and synchronously. Therefore, at least in the beginning of using library, it is the good practise to store <code>host</code> in the root of your component. As it may be changed, typically when there is asynchronous code in the component.</p><divclass="code"data-js="todo"><!--<dde:mark type="component" name="code" host="parentElement" ssr/>--><codeclass="language-js">import { el, scope, on, dispatchEvent } from "deka-dom-el";
document.body.append(
el(component)
);
function component(){
const { host }= scope; // good practise!
host(
console.log,
on("click", function redispatch(){
// this `host` ↘ still corresponds to the host ↖ of the component
dispatchEvent("redispatch")(host());
})
);
// this `host` ↘ still corresponds to the host ↖ of the component
</code></div><h3id="h-scopes-observables-and-cleaning-magic"><!--<dde:mark type="component" name="h3" host="parentElement" ssr/>--><ahref="#h-scopes-observables-and-cleaning-magic"tabindex="-1">#</a> Scopes, observables and cleaning magic</h3><p>The <code>host</code> is internally used to register the cleaning procedure, when the component (<code>host</code> element) is removed from the DOM.</p><!--<dde:mark type="component" name="example" host="this" ssr/>--><divid="code-example-1-5am55s7aitw"class="example"><!--<dde:mark type="component" name="code" host="parentElement" ssr/>--><codeclass="language-js">import { el, empty } from "https://cdn.jsdelivr.net/gh/jaandrle/deka-dom-el/dist/esm-with-observables.js";
document.body.append(
el(component),
el("button", {
textContent: "Remove",
onclick: ()=> empty(document.body),
type: "button"
})
);
import { on } from "https://cdn.jsdelivr.net/gh/jaandrle/deka-dom-el/dist/esm-with-observables.js";
import { O } from "https://cdn.jsdelivr.net/gh/jaandrle/deka-dom-el/dist/esm-with-observables.js";
function component(){
const textContent= O("Click to change text.");
const onclickChange= on("click", function redispatch(){
</code></div><script>Flems(document.getElementById("code-example-1-5am55s7aitw"),JSON.parse("{\"files\":[{\"name\":\".js\",\"content\":\"import { el, empty } from \\\"https://cdn.jsdelivr.net/gh/jaandrle/deka-dom-el/dist/esm-with-observables.js\\\";\\ndocument.body.append(\\n\\tel(component),\\n\\tel(\\\"button\\\", {\\n\\t\\ttextContent: \\\"Remove\\\",\\n\\t\\tonclick: ()=> empty(document.body),\\n\\t\\ttype: \\\"button\\\"\\n\\t})\\n);\\nimport { on } from \\\"https://cdn.jsdelivr.net/gh/jaandrle/deka-dom-el/dist/esm-with-observables.js\\\";\\nimport { O } from \\\"https://cdn.jsdelivr.net/gh/jaandrle/deka-dom-el/dist/esm-with-observables.js\\\";\\nfunction component(){\\n\\tconst textContent= O(\\\"Click to change text.\\\");\\n\\n\\tconst onclickChange= on(\\\"click\\\", function redispatch(){\\n\\t\\ttextContent(\\\"Text changed! \\\"+(new Date()).toString())\\n\\t});\\n\\treturn el(\\\"p\\\", textContent, onclickChange);\\n}\\n\"}],\"toolbar\":false}"));</script><p>The text content of the paragraph is changing when the value of the observable <code>textContent</code> is changed. Internally, there is association between <code>textContent</code> and the paragraph similar to using <code>S.on(textContent, /* update the paragraph */)</code>.</p><p>This listener must be removed when the component is removed from the DOM. To do it, the library assign internally <code>on.disconnected(/* remove the listener */)(host())</code> to the host element.</p><pclass="notice">The library DOM API and observables works ideally when used declaratively. It means, you split your app logic into three parts as it was itroduced in <ahref="http://localhost:40911/docs/p04-observables#h-introducing-observables">Observables</a>.</p><divclass="code"data-js="todo"><!--<dde:mark type="component" name="code" host="parentElement" ssr/>--><codeclass="language-js">/* PSEUDO-CODE!!! */
</code></div><p>Strictly speaking, the imperative way of using the library is not prohibited. Just be careful (rather avoid) mixing declarative approach (using observables) and imperative manipulation of elements.</p><divclass="code"data-js="todo"><!--<dde:mark type="component" name="code" host="parentElement" ssr/>--><codeclass="language-js">/* PSEUDO-CODE!!! */
</code></div><divclass="notice"><!--<dde:mark type="component" name="mnemonic" host="parentElement" ssr/>--><h3id="h-mnemonic"><!--<dde:mark type="component" name="h3" host="parentElement" ssr/>--><ahref="#h-mnemonic"tabindex="-1">#</a> Mnemonic</h3><ul><li><code>el(<function>, <function-argument(s)>)[.append(...)]: <element-returned-by-function></code> — using component represented by function</li><li><code>scope.host()</code> — get current component reference</li><li><code>scope.host(...<addons>)</code> — use addons to current component</li></ul></div><divclass="prevNext"><!--<dde:mark type="component" name="prevNext" host="parentElement" ssr/>--><arel="prev"href="p04-observables"title="Handling reactivity in UI via observables."><!--<dde:mark type="component" name="pageLink" host="parentElement" ssr/>-->Observables and reactivity (previous)</a><arel="next"href="p06-customElement"title="Using custom elements in combinantion with DDE"><!--<dde:mark type="component" name="pageLink" host="parentElement" ssr/>-->(next) Custom elements</a></div></main></body></html>
