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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="Organizing UI into components"><title>`deka-dom-el` — Scopes and components</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` — Scopes and components</h1><p>Organizing UI into components</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&nbsp;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.">4. Observables and reactivity</a><a href="p05-scopes" title="Organizing UI into components" class="current">5. Scopes and components</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 <a href="https://developer.mozilla.org/en-US/docs/Glossary/Garbage_collection" title="Garbage collection | MDN">Garbage collection</a>.</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
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import { scope, el } from "deka-dom-el";
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/** @type {ddeElementAddon} */
</code></div><p>The library therefore use <em>scopes</em> to provide these functionalities.</p><h3 id="h-scopes-and-hosts"><!--<dde:mark type="component" name="h3" host="parentElement" ssr/>--><a href="#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(...&lt;addons&gt;)</code>.</p><!--<dde:mark type="component" name="example" host="this" ssr/>--><div id="code-example-1-8meex5b3tyo" class="example"><!--<dde:mark type="component" name="code" host="parentElement" ssr/>--><code class="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=&gt; 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=&gt; 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",
host().outerHTML
);
})
return el("div", null, onclick).append(
el("strong", "Component")
);
}
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</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/>--><div id="code-example-3-b6a1hbrxh7s" class="example"><!--<dde:mark type="component" name="code" host="parentElement" ssr/>--><code class="language-js">import { el } from "https://cdn.jsdelivr.net/gh/jaandrle/deka-dom-el/dist/esm-with-observables.js";
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class Test {
constructor(params){
this._params= params;
}
render(){
return el("div").append(
this._params.textContent
);
}
}
document.body.append(
elClass(Test, { textContent: "Hello World" })
);
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import { chainableAppend, scope } from "https://cdn.jsdelivr.net/gh/jaandrle/deka-dom-el/dist/esm-with-observables.js";
function elClass(_class, attributes, ...addons){
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let element, element_host;
scope.push({
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scope: _class, //just informative purposes
host: (...addons_append)=&gt; addons_append.length
? (
!element
? addons.unshift(...addons_append)
: addons_append.forEach(c=&gt; c(element_host))
, undefined)
: element_host
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});
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const instance= new _class(attributes);
element= instance.render();
const is_fragment= element instanceof DocumentFragment;
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const el_mark= el.mark({ //this creates html comment `&lt;dde:mark …/&gt;`
type: "class-component",
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name: _class.name,
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host: is_fragment ? "this" : "parentElement",
});
element.prepend(el_mark);
if(is_fragment) element_host= el_mark;
chainableAppend(element);
addons.forEach(c=&gt; c(element_host));
scope.pop();
return element;
}
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</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><div class="code" data-js="todo"><!--<dde:mark type="component" name="code" host="parentElement" ssr/>--><code class="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
setTimeout(()=&gt; dispatchEvent("timeout")(host()), 750)
return el("p", "Clickable paragraph!");
}
</code></div><h3 id="h-scopes-observables-and-cleaning-magic"><!--<dde:mark type="component" name="h3" host="parentElement" ssr/>--><a href="#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/>--><div id="code-example-1-5am55s7aitw" class="example"><!--<dde:mark type="component" name="code" host="parentElement" ssr/>--><code class="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: ()=&gt; 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(){
textContent("Text changed! "+(new Date()).toString())
});
return el("p", textContent, onclickChange);
}
:memo: update scopes documentation
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</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><p class="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 <a href="http://localhost:40911/docs/p04-observables#h-introducing-observables">Observables</a>.</p><div class="code" data-js="todo"><!--<dde:mark type="component" name="code" host="parentElement" ssr/>--><code class="language-js">/* PSEUDO-CODE!!! */
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import { el } from "deka-dom-el";
import { O } from "deka-dom-el/observables";
function component(){
/* prepare changeable data */
const dataA= O("data");
const dataB= O("data");
/* define data flow (can be asynchronous) */
fetchAPI().then(data_new=&gt; dataA(data_new));
setTimeout(()=&gt; dataB("DATA"));
/* declarative UI */
return el().append(
el("h1", {
textContent: "Example",
/* declarative attribute(s) */
classList: { declarative: dataB }
}),
el("ul").append(
/* declarative element(s) */
O.el(dataA, data=&gt; data.map(d=&gt; el("li", d)))
),
el("ul").append(
/* declarative component(s) */
O.el(dataA, data=&gt; data.map(d=&gt; el(subcomponent, d)))
)
);
}
function subcomponent({ id }){
/* prepare changeable data */
const textContent= O("…");
/* define data flow (can be asynchronous) */
fetchAPI(id).then(text=&gt; textContent(text));
/* declarative UI */
return el("li", { textContent, dataId: id });
}
</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><div class="code" data-js="todo"><!--<dde:mark type="component" name="code" host="parentElement" ssr/>--><code class="language-js">/* PSEUDO-CODE!!! */
import { el, on, scope } from "deka-dom-el";
function component(){
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const { host }= scope;
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const ul= el("ul");
const ac= new AbortController();
fetchAPI({ signal: ac.signal }).then(data=&gt; {
data.forEach(d=&gt; ul.append(el("li", d)));
});
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host(
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/* element was remove before data fetched */
on.disconnected(()=&gt; ac.abort())
);
return ul;
/**
* NEVER EVER!!
* let data;
* fetchAPI().then(d=&gt; data= O(d));
*
* OR NEVER EVER!!
* const ul= el("ul");
* fetchAPI().then(d=&gt; {
* const data= O("data");
* ul.append(el("li", data));
* });
*
* // THE HOST IS PROBABLY DIFFERENT THAN
* // YOU EXPECT AND OBSERVABLES MAY BE
* // UNEXPECTEDLY REMOVED!!!
* */
}
</code></div><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>el(&lt;function&gt;, &lt;function-argument(s)&gt;)[.append(...)]: &lt;element-returned-by-function&gt;</code> — using component represented by function</li><li><code>scope.host()</code> — get current component reference</li><li><code>scope.host(...&lt;addons&gt;)</code> — use addons to current component</li></ul></div><div class="prevNext"><!--<dde:mark type="component" name="prevNext" host="parentElement" ssr/>--><a rel="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><!--<dde:mark type="component" name="pageLink" host="this" ssr/>--></div></main></body></html>
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