External Link Check

external-link-check.js

function isExternal(url) {
    var match = url.match(/^([^:\/?#]+:)?(?:\/\/([^\/?#]*))?([^?#]+)?(\?[^#]*)?(#.*)?/);
    if (typeof match[1] === "string" && match[1].length > 0 && match[1].toLowerCase() !== location.protocol) return true;
    if (typeof match[2] === "string" && match[2].length > 0 && match[2].replace(new RegExp(":("+{"http:":80,"https:":443}[location.protocol]+")?$"), "") !== location.host) return true;
    return false;
}