extendTag in Dart custom element

问题:

from this link in javascript, customs element extending button is made as:

var MegaButton = document.registerElement('mega-button', {
  prototype: Object.create(HTMLButtonElement.prototype),
  extends: 'button'
});

<button is="mega-button">

I tried making the same using dart, by this code:

class MegaButton extends ButtonElement  {
static final tag = 'mega-button';
factory MegaButton()=>new Element.tag('button', tag);  
   MegaButton.created() : super.created() { 
       var shadow = this.createShadowRoot();
       shadow.text='save';
  }
}
 document.registerElement(MegaButton.tag, MegaButton);

in the html file

    <button  is="mega-button"></button>
    <mega-button>click me</mega-button>

but got this error:

Exception: Unsupported operation: Class must provide extendsTag if base native class is not HTMLElement

any help pls. thanks

回答1:

document.registerElement should look like:

document.registerElement(MegaButton.tag, MegaButton, extendsTag: 'button');

=> new Element.tag('button', tag);

see also Custom Polymer element extending AElement in Dart

回答2:

The below code worked perfectly with me:

class SaveBtn extends HtmlElement  {
       static final tag = 'save-button';
       factory SaveBtn()=>new Element.tag(tag); 

    SaveBtn.created() : super.created() {
    //  Create a Shadow Root
    var shadow = this.createShadowRoot();
   // Create a standard element and set it's attributes.
   var btn = new ButtonElement()
    ..style.height= '20px'  
    ..style.width= '50px'
    ..style.color= '#FF8F66'
    ..style.border='1px solid #BCC1C8'
    ..style.background='#F1F4FB'  
    ..style.borderRadius='5px'
    ..style.fontFamily='openSansItalic' 
    ..style.fontSize='12px'
    ..style.padding='0px 6px'
    ..style.marginLeft='0.1em'  
    ..style.borderBeforeStyle='solid'
    ..style.borderWidth='1px'
    ..style.borderColor='transparent'
    ..style.marginBottom='2px'
    ..style.borderBottom='1px solid #D1DBE9'; 

   btn.text= this.getAttribute('data-name');

   btn.onMouseDown.listen((e){ 
      btn..style.color="#333"
     ..style.background='#FF8F66';
    });
   btn.onMouseUp.listen((e){ 
   btn..style.color="#FF8F66"
     ..style.background='#F1F4FB'
     ..style.outline='none';  // remove the focus outline/glur
    });
   btn.onMouseEnter.listen((e)=> btn..style.boxShadow='0px 0px 5px #888888');
   btn.onMouseLeave.listen((e)=> btn..style.boxShadow='0px 0px 0px');

   if(btn.disabled==true){
     btn..style.color="gray";
   }
   shadow.nodes.add(btn);

   Element launchElement(){ 
     return (shadow); 
    }

  }  
 }

the custom element registration:

document.registerElement(SaveBtn.tag, SaveBtn);

and in the html file, I used:

<save-button data-name='save orders'></save-button>