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How to create new instance of an extended class of custom elements

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隐瞒了意图╮
隐瞒了意图╮ 2020-11-30 12:51

I\'m trying the example from google developer site and I\'m getting Error: \"TypeError: Illegal constructor. What\'s wrong and How to fix it?

class FancyButt
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  • 半阙折子戏
    2020-11-30 13:33 
    class F_BTN extends HTMLButtonElement{
    constructor(){
        super(); // must call constructor from parent class
        this.addEventListener(...);
        .... // etc.
     }
}

customElements.define("f-btn",F_BTN,{extends:'button'});

    use inline:

    <body>  ....  <f-btn>BTN_NAME</f-btn>  ...  </body>

    or create append from javascript

    var elm = new F_BTN(...options); 
// F_BTN = customElements.get('f-btn') // in case F_BTN is out of scope

    The problem is elm = document.createElement('f-btn') doesn't work.

    That is why I made my custom create_element function _E

    _E = function (name, html) {
  var $;
  switch (true) {
    case (name === '' || !name):  // _E()  -- a div
        {
            $ = document.createElement('div');
        }
        break; 
    case (!name.indexOf('<')):  // _E('<h1><i>abc</i><b>A</b></h1>')  -- sub_dom
        {
            $ = document.createElement('div');
            $.innerHTML = name;
            $ = $.firstElementChild;
        }
        break;
    default:
        var c = window.customElements.get(name);
        if(c){ 
          $ = new c();   // _E('f-btn')  -- customElement
        } else {
          $ = document.createElement(name); // _E('button')  -- htmlElement
        }   
  }      
  if (html) $.innerHTML = html;
  return $;
};

var elm1 = _E('f-btn'); parent.appendChild(elm1);
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  • 无人及你
    2020-11-30 13:35

    Blink, the web engine that currently implements Custom Element v1 (in Chrome v53+ for example) only supports autonomous custom elements: see open Blink bug.

    If you want to define customized built-in elements (i.e. <button> extension), you'll need to use a polyfill like the one from Web Reflection.

    Alternatly, you can still use the Custom Element v0 syntax (document.registerElement).

    Update #3

    Since october 2018, they work natively with Chrome 67+ and Firefox 63+ :-)

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