Is it possible to use the new Clipboard API in a GWT app? It depends on document.hasFocus being true.

Ok, there are a few moving parts to this. Keeping it as short as possible, this is the new Clipboard API:

https://developer.mozilla.org/en-US/docs/Web/API/Clipboard

Support is extremely limited at the moment, but for now I'd be happy to get something working in Chrome:

https://caniuse.com/#feat=mdn-api_clipboard

Here's Google's live sample page:

https://googlechrome.github.io/samples/async-clipboard/index.html

For obvious reasons, there's a lot of paranoid security around JavaScript access to the clipboard. This is the specific detail I'm running into:

https://stackoverflow.com/questions/56306153/domexception-on-calling-navigator-clipboard-readtext

These APIs throw a security exception if document.hasFocus() is false. And I'm not seeing any way to honour that rule in a GWT app. In my production app, and in a tiny standalone GWT app I just generated for testing purposes, document.hasFocus() is always false ($doc.hasFocus() is true).

For testing purposes, I generated the GWT StockWatcher demo app:

http://www.gwtproject.org/doc/latest/tutorial/create.html

Then I added some UI hooks for clipboard testing elements in StockWatcher.html:

    <h1>Web Application Starter Project</h1>

    <table align="center">

      <tr>

        <td colspan="2" style="font-weight:bold;">Please enter your name:</td>        

      </tr>

      <tr>

        <td id="nameFieldContainer"></td>

        <td id="sendButtonContainer"></td>

      </tr>

      <tr>

        <td colspan="2" style="color:red;" id="errorLabelContainer"></td>

      </tr>

      <tr>

        <td id="readTextField"></td>

        <td id="readTextButton"></td>

      </tr>      

      <tr>

        <td id="writeTextField"></td>

        <td id="writeTextButton"></td>

      </tr>

    </table>

And minimal testing UI in StockWatcher.java onModuleLoad:

        TextBox readText = new TextBox();

        readText.setText("readText");

        Button readTextButton = new Button("readText");

        TextBox writeText = new TextBox();

        writeText.setText("writeText");

        Button writeTextButton = new Button("writeText");

        

        RootPanel.get("readTextField").add(readText);

        RootPanel.get("readTextButton").add(readTextButton);

        

        RootPanel.get("writeTextField").add(writeText);

        RootPanel.get("writeTextButton").add(writeTextButton);

        readTextButton.addClickHandler(new ClickHandler()

        {

            public void onClick(ClickEvent event)

            {

                readText();

            }

        });

        

        writeTextButton.addClickHandler(new ClickHandler()

        {

            public void onClick(ClickEvent event)

            {

                writeText(writeText.getText());

            }

        });

And corresponding JSNI functions to attempt to invoke the Clipboard API:

   

    public native void readText()

    /*-{

        try

        {

            if (navigator.clipboard)

            {

                console.log('navigator.clipboard.readText()');

                console.log('document.hasFocus()='+document.hasFocus());

                console.log('$doc.hasFocus()='+$doc.hasFocus());

                var promise = navigator.clipboard.readText();

                var resolve = function(text) {

                    console.log(text);

                };

                var reject = function(reason) {

                    console.log('navigator.clipboard.readText failed: '+reason);

                };

                promise["catch"](reject);

                promise.then(resolve,reject)["catch"](reject);

            }

            else

            {

                console.log('This browser does not support navigator.clipboard.');

            }

        }

        catch (e)

        {

            console.error(e,e.stack);

        }

    }-*/;

    

    public native void writeText(String p_text)

    /*-{

        try

        {

            var _this = this;

            if (navigator.clipboard)

            {

                console.log('navigator.clipboard.writeText()');

                console.log('document.hasFocus()='+document.hasFocus());

                console.log('$doc.hasFocus()='+$doc.hasFocus());

                var promise = navigator.clipboard.writeText(p_text);

                var resolve = function(text) {

                    console.log('navigator.clipboard.writeText '+text);

                };

                var reject = function(reason) {

                    console.log('navigator.clipboard.writeText failed: '+reason);

                };

                promise["catch"](reject);

                promise.then(resolve,reject)["catch"](reject);

            }

            else

            {

                console.log('This browser does not support navigator.clipboard.');

            }

        }

        catch (e)

        {

            console.error(e,e.stack);

        }

    }-*/;

And I'm stuck on the same security error noted in that StackOverflow question, but with no obvious way to satisfy that requirement:

navigator.clipboard.readText()

document.hasFocus()=false

$doc.hasFocus()=true

navigator.clipboard.readText failed: NotAllowedError: Document is not focused.

navigator.clipboard.writeText()

document.hasFocus()=false

$doc.hasFocus()=true

navigator.clipboard.writeText failed: NotAllowedError: Document is not focused.

Is there any way to make this work in GWT?

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