快速實現複製到剪貼板

<p>點擊複製後在右邊textarea CTRL+V看一下</p>
<input type="text" id="inputText" value="測試文本"/>
    <input type="button" id="btn" value="複製"/>
    <textarea rows="4"></textarea>
    <script type="text/javascript">
var btn = document.getElementById('btn');
btn.addEventListener('click', function(){
    var inputText = document.getElementById('inputText');
    var currentFocus = document.activeElement;
    inputText.focus();
    inputText.setSelectionRange(0, inputText.value.length);
    document.execCommand('copy', true);
    currentFocus.focus();
});