使用RegExp构造函数代替正则表达式文字.

Use the RegExp constructor instead of regex literal.

var regex = new RegExp("<" + tagname + ">(.*)</" + tagname + ">", "gi");
$("textarea").val().replace(regex, "<" + tagname + ">" + 
   textVariable + "</" + tagname + ">");

您可以将其简化为:

//capture the tag name:
var regex = new RegExp("<(" + tagname + ")>(.*)</" + tagname + ">", "gi");
$("textarea").val().replace(regex, "<$1>" + textVariable + "</$1>");

但请记住，解析xml /html和regex是一个好主意