1.select事件 选中默认值 出发点是让用户能够一次性删除所有默认内容
<html>
<head></head>
<body>
<form action="">
<input type="text" size="25" maxlength="50" name="inputOne" id="" value="initial value">
</form>
<script>
const textbox = document.forms[0].elements['inputOne']
console.log(textbox);
console.log(textbox.value);
textbox.select()
</script>
</body>
</html>