用于检查选项列表验证的函数不起作用

Question

我有一个表单的选择选项列表，我想确保用户已经选择了其中一个选项。我的功能逻辑意味着，如果用户将下拉列表保留在默认选项上，就会弹出一条警告，提示他们更改它。然而，不会显示任何警告。我做错了什么？

function isOption(form) {
var type = form.getElementByID("pastimetype")
var selectedValue = type.options[type.selectedIndex].value;
if (selectedValue == "selectpastime") {
alert("Please select a pastime.")
return false
}
return true
}

<p><label for="pastime"> Favourite pastime: </label>
<select name="pastime" select id="pastimetype">
<option value="selectpastime">---Please choose an option---</option>
<option value="surfingtheweb">Surfing the Web</option>
<option value="playingsport">Playing Sport</option>
<option value="listeningtomusic">Listening to Music</option>
<option value="watchingtv">Watching TV</option>
<option value="playinggames">Playing Games</option>
<option value="communityservice">Community Service</option>
<option value="daydreaming">Daydreaming</option>
<option value="reading">Reading</option>
<option value="meditation">Meditation</option>
</select>
</p>

Answer 1

• 您需要将函数添加到表单的提交事件中
• 您拼错了getElementById
• 无需使用form.getElementById
• 使用select.value更容易获取值
• 使用preventDefault而不是返回true/false

还有

function isOption(e) {
var sel = document.getElementById("pastimetype");
var selectedValue = sel.value;
if (selectedValue == "") { // I removed the value from the "Please select"
alert("Please select a pastime.")
e.preventDefault(); // stop submission
}
}
window.addEventListener("load",function() {
document.getElementById("form1").addEventListener("submit",isOption)
})

<form id="form1">
<p><label for="pastime"> Favourite pastime: </label>
<select name="pastime" select id="pastimetype">
<option value="">---Please choose an option---</option>
<option value="surfingtheweb">Surfing the Web</option>
<option value="playingsport">Playing Sport</option>
<option value="listeningtomusic">Listening to Music</option>
<option value="watchingtv">Watching TV</option>
<option value="playinggames">Playing Games</option>
<option value="communityservice">Community Service</option>
<option value="daydreaming">Daydreaming</option>
<option value="reading">Reading</option>
<option value="meditation">Meditation</option>
</select>
</p>
<input type="submit" />
</form>