JSFiddle - React, Tailwind, and code Playground

JavaScript

var s = '<a href="http://www.abc.com/thisSite/myPages/blah-blah-blah.aspx">http://www.abc.com/thisSite/myPages/blah-blah-blah.aspx</a>';
var t = s.replace(/(<a [^>]*>)([^<]{1,20})([^<]*)(<\/a>)/, function(str, p1, p2, p3, p4) {
    return p1 + p2 + (p3.length ? '...' : '') + p4;
});
document.write(t);