Allow programmatic copy to clipboard

[Madhu94]

Trying to close #2975.

@takluyver I did not go with document.execCommand because it does not allow you to set a mime-types like html, json, etc. (or I couldn't find a way to do that anyway) and I see you need that.

Let me know if these changes are okay.

[Madhu94]

This works for my usecase, in both Chrome and FF. But I see that you can't actually test this...I'll come up with a reproducible test case.

[Madhu94]

@takluyver Here is an example you can paste into a notebook cell to reproduce this bug and see what this fix does.

class copytoclipboard(object):
    def _repr_html_(self):
        return """
            <button class="btn">Copy to clipboard</button>
            <script>
                function copyToClipboard(copytext) {
                    var ta = document.createElement('textarea');
                    ta.value = copytext;
                    ta.style.position = 'absolute';
                    ta.style.left = '-9999px';
                    document.body.append(ta);
                    ta.select()
                    ta.focus();
                    console.log("Attempting to copy" + copytext);
                    var success=document.execCommand('copy');
                    console.log(success);
                    
                }
                $('.btn').click(function(){
                  copyToClipboard("Ho ho");
                })
            </script>
        """
copytoclipboard()

[gnestor]

I tested and it works! Looks good to me.

@takluyver Care to merge?

[takluyver]

Thanks, I've also tested this, and it seems to be fine.

For my own understanding, why does the existing window.getSelection().isCollapsed check not do the same? Is the invisible text field ignored when finding window.getSelection()?

[Madhu94]

@takluyver window.getSelection().isCollapsed would not return True if, in the above example, you were to set ta.innerHTML to the copytext and not ta.value.

I don't find it intuitive either.

[takluyver]

Fair enough. Browsers are strange.

[takluyver]

By the way, thanks for providing the example so we could easily test what you meant!