<time-formatted>

📗 參考

• 📗 Example: “time-formatted” (JS.info)

• 📘 Intl.DateTimeFormat (MDN)

• 💾 replit

📘 手冊

• element.getAttribute(name) (MDN)

• element.setAttribute(name, value) (MDN)

• Google ⟩ Custom Element Upgrades

Custom Element Upgrade

The process of calling customElements.define() and endowing an existing element with a class definition is called "element upgrades". 📘 Google ⟩ Element Upgrades

If browser encounters<time-formatted>elements beforecustomElements.define, the element is yet unknown, just like any non-standard tag.

• undefined elements can be styled with CSS selector:not(:defined).

When customElement.define is called, they are “upgraded”: a new instance of TimeFormatted is created for each, and connectedCallback is called.

• They become :defined. 👉 pseudo-class

code

JS

// ⭐️ get/set attribute
//    get: elem.attr(name)
//    set: elem.attr(name, value)
Element.prototype.attr = function(name, value=undefined){
    if(value !== undefined){ this.setAttribute(name, value) };
    return this.getAttribute(name) || undefined;
};

// 1. define new element
class TimeFormatted extends HTMLElement {

    /* ---------- life cycle callbacks ---------- */

    // triggers when <time-formatted> element is added to page
    // (or when HTML parser detects it)
    connectedCallback() {
        this.render();
    }

    // observed attributes
    static get observedAttributes() { // (3)
        return [
            'datetime', 'year', 'month', 'day', 
            'hour', 'minute', 'second', 'time-zone-name'
        ];
    }

    attributeChangedCallback(name, oldValue, newValue) { 
        // re-render when attributes changed
        this.render();
    }

  /* ---------- helper methods ---------- */
  
    render() {

        let date = new Date(this.attr('datetime') || Date.now());

        // built-in Intl.DateTimeFormat formatter
        let formatter = new Intl.DateTimeFormat("default", {
        year  : this.attr('year'),
        month : this.attr('month'),
        day   : this.attr('day'),
        hour  : this.attr('hour'),
        minute: this.attr('minute'),
        second: this.attr('second'),
        timeZoneName: this.attr('time-zone-name'),
        });

        // show a nicely formatted time.
        // ⭐️ 注意：這裡設定的東西屬於 light DOM❗️
        this.innerHTML = formatter.format(date);
    }
}

// 2. register new element
customElements.define("time-formatted", TimeFormatted);

// change attribute 'datetime' per second.
setInterval(
    () => elem.attr('datetime', new Date()), 
    1000
);

HTML

<time-formatted 
	id="elem"
	datetime="2019-12-01" 
	year="numeric" 
	month="long" 
	day="numeric" 
	hour="numeric" 
	minute="numeric" 
	second="numeric"
	time-zone-name="short">
</time-formatted>

📗 參考