Could anybody help me solving this problem?

I create html form for your code ??
https://jsfiddle.net/NeoCsatornaja/Bdy9n/3/

Check this: https://jsfiddle.net/grRPw/8/

I found the solution and i like to show!
Html:

<p>
	<label for="ytlink">Youtube.com/watch?v=</label>
	<input type="text" id="yt_link" name="ytlink" />
	<label for="ytlinkname">Video name:</label>
	<input type="text" id="yt_link_name" name="ytlinkname" />
	<input type="button" id="btn1" value="Video Paste" onclick="yt_link_transfer();" />
</p>
<p>
	<label for="link">https://</label>
	<input type="text" id="link" name="link" />
	<label for="linkname">Link name:</label>
        <input type="text" id="link_name" name="linkname"/>
        <input type="button" id="btn2" value="Link Paste" onclick="link_transfer();" />
</p>
<input type="textarea" id="comment">

Head with jqvery:

function yt_link_transfer(){document.getElementById("comment").value += '<a href="https://www.youtube.com/embed/';document.getElementById("comment").value += document.getElementById("yt_link").value;document.getElementById("comment").value += '?autoplay=1';document.getElementById("comment").value += '" class="lightview">';document.getElementById("comment").value += document.getElementById("yt_link_name").value;document.getElementById("comment").value += '</a> ';}function link_transfer(){document.getElementById("comment").value += '<a href="https://';document.getElementById("comment").value += document.getElementById("link").value;document.getElementById("comment").value += '" class="lightview">';document.getElementById("comment").value += document.getElementById("link_name").value;document.getElementById("comment").value += '</a> ';}

Thx for the support and work everyone,special thanks for:
Ihor Vorotnov, you’re best!

The script does basically the same but with pure javascript (my version was for jQuery). And separating YouTube and Link inputs is logical. Glad you managed to make it work! Good luck! ??

thx for the support.
Can you share this the popular site?
Sure many people will be looking for.
Otherwise, jquery 2.0 works alone, so be sure to add: D
if you think create the plugin this and lightview:D