我还有另一个问题。如何将输入表单限制为仅接受来自某个网站的链接，例如Youtube应该包含此链接https://www.youtube.com/---，并且通过单击添加按钮，您将只允许列表中的该类型的链接。我到处都看过，但是什么也找不到。
<script>
var input = document.getElementById('geturl');
var button = document.getElementById('addlist');
var addurl = function() {
var url = input.value;
var li = document.createElement('li');
li.innerHTML = url;
song = document.getElementById('songurl');
if (url.length == 0) {
alert('Please input data in the field.');
console.log('No text in input.');
} else {
song.appendChild(li);
document.getElementById("geturl").value = "";
console.log('Url added');
}
}
button.onclick = addurl;
</script>
</-->
<body>
<header>
<nav>
<div class="vidplay-title">
<div class="logo">
<i class="fa fa-forward" style="font-size:24px"></i>
</div>
<div class="title">
<h2>Music Share</h2>
</div>
</div>
</nav>
</header>
<section id="content">
<form name="form">
<div class="search">
<input type="text" placeholder="paste url..." id="geturl">
<input type="submit" value="Add" id="addlist" onclick="return empty()" name="url">
</div>
<article>
<div class="container" id=#list>
<h5>Share your youtube url list and enjoy.</h5>
<div class="scroll list-item-group">
<div class="song-list">
<ol class="song" id="songurl">
</div>
</div>
<button class="btn btn-primary">Share</button>
</article>
</div>
</form>
</section>
<section>
<footer>
<div class="footer">
<p>@Copyright</p>
</div>
</footer>
</section>
startsWith()（或正则表达式）：if (url.length == 0) {
alert('Please input data in the field.');
return;
}
if (!url.startsWith("https://www.youtube.com/")) {
alert("Not a YouTube link.");
return;
}
song.appendChild(li);
document.getElementById("geturl").value = "";
// etc...