caveats

[webcomponents]

caveats

[Shijir]

I am using Typescript. And I had to use the following constructor to make it work.

constructor() {
    return super();
}

[bicknellr]

I'm confused about what the upgrade for procedurally created elements refers to:

The current standard cannot possibly be polifilled "1:1" with vanilla JavaScript because procedurally created instances need an upgrade.

As far as I know, the main problem with CE v1 and polyfills is that you can't actually write a definition that doesn't use ES2015 that also works with a native implementation. Specifically, to construct a native custom element, you must either write it with class syntax and call super(); or use Reflect.construct and pass new.target - both of which are syntax errors in ES5.

Is this demo something like what you were asking about in the original question: http://jsbin.com/tapoqam/1/edit?html,output ?

[trusktr]

@bicknellr It means that the instance of your element will go from instanceof HTMLUnknownElement to instanceof YourCustomElement magically, and your reference to it in your code (and in the DOM) will be the same reference. This magic happens on the native (C/C++) side of the engine, not really polyfillable.

[trusktr]

@bicknellr Your example works fine because (I believe?) the polyfill just detects and uses the native implementation. But if you add transpiling (es6+ -> es5) then you run into the issues having to ironically use Reflect.construct, etc, even though it isn't es5, because it needs to work when the polyfill detects the native implementation. Transpilation should work fine in a 100% es5 poyfill I think (just guessing, haven't tried yet).

[dfreedm]

README has some caveats for classes with es5 transpilation, this likely should have been closed when that was added.