mirror of
https://github.com/jaandrle/deka-dom-el
synced 2024-11-23 00:59:38 +01:00
104 lines
6.0 KiB
JavaScript
104 lines
6.0 KiB
JavaScript
import { simplePage } from "./layout/simplePage.html.js";
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import { el } from "deka-dom-el";
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import { example } from "./components/example.html.js";
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import { h3 } from "./components/pageUtils.html.js";
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import { mnemonic } from "./components/mnemonic/observables-init.js";
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import { code } from "./components/code.html.js";
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/** @param {string} url */
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const fileURL= url=> new URL(url, import.meta.url);
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/** @param {import("./types.d.ts").PageAttrs} attrs */
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export function page({ pkg, info }){
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const page_id= info.id;
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return el(simplePage, { info, pkg }).append(
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el("h2", "Using observables to manage reactivity"),
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el("p").append(
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"How a program responds to variable data or user",
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" interactions is one of the fundamental problems of programming.",
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" If we desire to solve the issue in a declarative manner,",
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" observables may be a viable approach.",
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),
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el(code, { src: fileURL("./components/examples/observables/intro.js"), page_id }),
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el(h3, "Introducing observables"),
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el("p").append(
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"Using observables, we split program logic into the three parts.",
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" Firstly (α), we create a variable (constant) representing reactive",
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" value. Somewhere later, we can register (β) a logic reacting",
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" to the observable value changes. Similarly, in a remaining part (γ), we",
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" can update the observable value."
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),
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el(example, { src: fileURL("./components/examples/observables/observables.js"), page_id }),
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el("p").append(
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"All this is just an example of ",
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el("a", { textContent: "Event-driven programming", href: "https://en.wikipedia.org/wiki/Event-driven_programming", title: "Wikipedia: Event-driven programming" }),
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" and ",
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el("a", { textContent: "Publish–subscribe pattern", href: "https://en.wikipedia.org/wiki/Publish%E2%80%93subscribe_pattern", title: "Wikipedia: Publish–subscribe pattern" }),
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" (compare for example with ", el("a", { textContent: "fpubsub library", href: "https://www.npmjs.com/package/fpubsub", title: "NPM package: fpubsub" }), ").",
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" All three parts can be in some manner independent and still connected",
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" to the same reactive entity."
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),
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el("p").append(
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"Observables are implemented in the library as functions. To see current value",
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" of observable, just call it without any arguments ", el("code", "console.log(observable())"), ".",
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" To update the observable value, pass any argument ", el("code", "observable('a new value')"), ".",
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" For listenning the observable value changes, use ", el("code", "O.on(observable, console.log)"), "."
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),
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el("p").append(
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"Similarly to the ", el("code", "on"), " function to register DOM events listener.",
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" You can use ", el("code", "AbortController"), "/", el("code", "AbortSignal"), " to",
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" ", el("em", "off"), "/stop listenning. In example, you also found the way for representing",
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" “live” piece of code computation pattern (derived observable):"
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),
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el(example, { src: fileURL("./components/examples/observables/computations-abort.js"), page_id }),
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el(h3, "Observables and actions"),
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el("p").append(
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el("code", "O(/* primitive */)"), " allows you to declare simple reactive variables, typically",
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" around ", el("em", "immutable"), " ", el("a", { textContent: "primitive types", title: "Primitive | MDN", href: "https://developer.mozilla.org/en-US/docs/Glossary/Primitive" }), ".",
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" ",
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"However, it may also be necessary to use reactive arrays, objects, or other complex reactive structures."
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),
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el(example, { src: fileURL("./components/examples/observables/actions-demo.js"), page_id }),
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el("p", "…but typical user-case is object/array (maps, sets and other mutable objects):"),
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el(example, { src: fileURL("./components/examples/observables/actions-todos.js"), page_id }),
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el("p").append(
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"In some way, you can compare it with ", el("a", { textContent: "useReducer", href: "https://react.dev/reference/react/useReducer", title: "useReducer hook | React docs" }),
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" hook from React. So, the ", el("code", "O(<data>, <actions>)"), " pattern creates",
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" a store “machine”. We can then invoke (dispatch) registered action by calling",
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" ", el("code", "O.action(<observable>, <name>, ...<args>)"), " after the action call",
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" the observable calls all its listeners. This can be stopped by calling ", el("code", "this.stopPropagation()"),
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" in the method representing the given action. As it can be seen in examples, the “store” value is",
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" available also in the function for given action (", el("code", "this.value"), ")."
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),
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el(h3, "Reactive DOM attributes and elements"),
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el("p", "There are on basic level two distinc situation to mirror dynamic value into the DOM/UI"),
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el("ol").append(
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el("li", "to change some attribute(s) of existing element(s)"),
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el("li", "to generate elements itself dynamically – this covers conditions and loops")
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),
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el(example, { src: fileURL("./components/examples/observables/dom-attrs.js"), page_id }),
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el("p").append(
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"To derived attribute based on value of observable variable just use the observable as",
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" a value of the attribute (", el("code", "assign(element, { attribute: O('value') })"), ").",
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" ", el("code", "assign"), "/", el("code", "el"), " provides ways to glue reactive attributes/classes",
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" more granularly into the DOM. Just use dedicated build-in attributes ", el("code", "dataset"), ", ",
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el("code", "ariaset"), " and ", el("code", "classList"), "."
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),
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el("p").append(
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"For computation, you can use the “derived observable” (see above) like ", el("code", "assign(element, { textContent: O(()=> 'Hello '+WorldObservable()) })"), ".",
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" ",
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"This is read-only observable its value is computed based on given function and updated when any observable used in the function changes."
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),
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el("p").append(
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"To represent part of the template filled dynamically based on the observable value use ", el("code", "O.el(observable, DOMgenerator)"), ".",
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" This was already used in the todo example above or see:"
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),
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el(example, { src: fileURL("./components/examples/observables/dom-el.js"), page_id }),
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el(mnemonic)
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);
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}
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