出處：
https://zhidao.baidu.com/question/77403775.html
<!doctype html>
<html>
<head>
<title>复制文本框</title>
</head>
<body>
<textarea id='text'></textarea>
<button id='copy' onclick=copy()>复制</button>
</body>
</html>
<script>
function copy(){
var text=document.getElementById('text');
var copy=document.getElementById('copy');
text.select();
document.execCommand("copy");
copy.focus();
alert("复制完成！")
}
</script>
