JSFiddle - React, Tailwind, and code Playground

HTML

<textarea name="" id="target" cols="30" rows="10"><%--targettarget

target

target--%></textarea>

JavaScript

var re = /(<%--)((?:.|\n)*)(--%>)/gmi; 
var str = document.getElementById('target').value;
var m;
 
while ((m = re.exec(str)) !== null) {
		alert(m[m.index]);
}