<!DOCTYPE html>
<html>
<head>
<script>
function myFunction()
{
document.getElementById("email").select();
}
</script>
</head>
<body>
<form>
Email: <input type="text" id="email" value="someone@example.com">
</form>
<button type="button" onclick="myFunction()">选取内容</button>
</body>
</html>
