[Webkit-unassigned] [Bug 174629] New: WKWebView issue when creating the web component paper-textarea element from document.createElement()

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=174629

            Bug ID: 174629
           Summary: WKWebView issue when creating the web component
                    paper-textarea element from document.createElement()
           Product: WebKit
           Version: Safari 10
          Hardware: iPhone / iPad
                OS: iOS 10.3
            Status: NEW
          Severity: Blocker
          Priority: P2
         Component: Bindings
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: marc.borntraeger at gmail.com
                CC: cdumez at apple.com

Original issue:
- https://github.com/PolymerElements/paper-input/issues/556
- https://github.com/hotforfeature/origami/issues/38

Our app gets called in two separate ways:
1. Like a normal web page through Google chrome
2. Through our native iOS app with WkWebView

So our approach was to build only a native app for iOS to fill the gaps of the ServiceWorker (like to enable push notifications, offline support, etc.). Which Safari, obviously doesn't have but chrome does.

On Google chrome (all versions) the app works without issues.
And on our Safari native app the web app crashes. Total crash happens without error message. So screen just gets blank.

We are using Angular and Polymer together. So this is why this issue came up -> **it only happens if a web component is created via** `document.createElement()`. So programmatically. Which Angular always does.

This is the browser version of WkWebView (verified with http://www.whoishostingthis.com/tools/user-agent/): `Mozilla/5.0 (iPhone; CPU iPhone OS 10_3_2 like Mac OS X) AppleWebKit/603.2.4 (KHTML, like Gecko) Mobile/14F89`

This is how we instantiate the paper-textarea:
```
<paper-textarea label="test" id="newMessage" name="newMessage"></paper-textarea>
```

The issue is only with paper-textarea. paper-input works perfectly

### Expected outcome

<!-- Example: The page stays the same color. -->

The app get's loaded correctly over WKWebView. Maybe there is something that `paper-textarea` does, which messes up the loading on WKWebView.

### Actual outcome

<!-- Example: The page turns pink. -->

# The Problem
Adding the <paper-textarea> to index.html was fine, but the Angular DefaultDomRenderer2 could not create it without throwing the error "A newly constructed custom element must not have attributes".

This is the cause for things breaking. While `document.createElement()` lets you continue, the element it returns is actually an `HTMLUnknownElement`, and so naturally it doesn't open its Shadow DOM from extending `Polymer.Element`.

# Raw vs Programmatic Element Creation

There are two ways to "create" an element: raw HTML and programatically. A Polymer project goes through raw HTML. It provides it directly to the browser to render.

Angular does things programmatically and calls `document.createElement()`. This is why you can do weird things like `<paper-item class$="[[binding]]">` in Polymer but not Angular. `class$` is not a valid attribute and throws an error when calling `element.setAttribute('class$', '[[binding]]')`.

# Not Just Angular!
So far, all the tests have just been isolated on `<paper-textarea>`. I'm testing with both this element and `<paper-input>`, since they're similar. `<paper-input>` is perfectly chill with `document.createElement()`.

I've ruled out Origami as the problem, so I thought maybe something with zone.js or the reflect shim was adding attributes at element creation. I decided to turn to pure Polymer and take both of these and any other weird Angular shenanigans out of the picture.

https://raw-dot-custom-elements.appspot.com/PolymerElements/paper-input/v2.0.0/paper-input/demo/index.html

This is the demo file that we should navigate to within the `WKWebView`. It'll load up just fine and `<paper-textarea>` works. Inspect the console and run the following:

```
window.onerror = function(err) { debugger; console.log('error', err) };
var ele = document.createElement('paper-textarea');
console.log(ele instanceof HTMLUnknownElement);
console.log(ele instanceof customElements.get('paper-textarea'));
```

Output:

```
[Log] error – "NotSupportedError (DOM Exception 9): A newly constructed custom element must not have attributes"
[Error] NotSupportedError (DOM Exception 9): A newly constructed custom element must not have attributes
        createElement
        Console Evaluation (Console Evaluation 4:3)
        evaluateWithScopeExtension
        _evaluateOn
        _evaluateAndWrap
        evaluate
[Log] true
[Log] false
```

# Thoughts
When creating a small component such as:
```
<dom-module id="paper-wrapped">
  <template>
    <paper-textarea value="{{value}}"></paper-textarea>
  </template>
  <script>
    Polymer({
      is: 'paper-wrapped',
      properties: {
        value: {
          type: String,
          notify: true      
       }
      }
    });
  </script>
</dom-module>
```
The whole concept works without problems. The website can be called via WKWebView.

We have ruled out the problem with the word "textarea". We thought maybe WKWebView sees that and is adding some textarea-specific attributes when it shouldn't be. But we tried it with this repo: https://github.com/BorntraegerMarc/paper-input which did not work as well.


### Live Demo
<!-- Example: https://jsbin.com/cagaye/edit?html,output -->
* https://github.com/kmyllyvi/WKWebViewTester
* https://github.com/BorntraegerMarc/polymer-chat
* https://raw-dot-custom-elements.appspot.com/PolymerElements/paper-input/v2.0.0/paper-input/demo/index.html

### Steps to reproduce

<!-- Example
1. Put a `paper-foo` element in the page.
2. Open the page in a web browser.
3. Click the `paper-foo` element.
-->

We ran the following tests:
1. We generated a normal polymer project with Polymer starter kit and everything worked as excpected. So the error only comes up if angular (or origami) is included
2. We created this minimal origami project: https://github.com/BorntraegerMarc/polymer-chat and the WKWebView crashes at the exact same component. Because of this: https://github.com/BorntraegerMarc/polymer-chat/blob/master/src/app/message/input/message-input.component.html#L3
3. If you completely comment out the `paper-textarea` component from the HTML it works without issue. So the TS reference `@ViewChild('messageInput')` has no influence on it. when we commented out `@ViewChild` the same issue persisted. Ony when commenting out the HTML code the app started to work again.

For easy testing purposes we created the following iOS native app project: https://github.com/kmyllyvi/WKWebViewTester you can just clone & run it.
Which is just a WKWebView project. How to test:
1. Clone and install the minimal origami project
2. Clone and install the WKWebView project
3. Start angular with ng serve
4. Start the ios app project on an iPhone simulator and navigate to http://localhost:3000 (you can enter the URL in the actual app)

### Browsers Affected
<!-- Check all that apply -->
- [ ] Chrome
- [ ] Firefox
- [X] WKWebView on all safari versions
- [ ] Safari 9
- [ ] Safari 8
- [ ] Safari 7
- [ ] Edge
- [ ] IE 11
- [ ] IE 10

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