alert will trigger keyboard

[Zuckjet]

I want to control clipboard content by javascript: 

```
<button id="btn">copy</button>
<script src="./index.js"></script>


var btn2 = document.getElementById('btn');
btn2.addEventListener('click', copy, false);



function copy() {
        let textArea = document.createElement("textarea");
        textArea.value = "copy content";
        document.body.appendChild(textArea);
        textArea.focus();
        textArea.select();

        document.execCommand("copy");
        alert("copy success");        // !!! this line will trigger keyboard, and make page response slowly, if i remove this line, everything is ok.
        document.body.removeChild(textArea);
}

```

[Radar WebKit Bug Importer]

<rdar://problem/79321330>