Extracted from validator.js (https://github.com/chriso/validator.js)

isValidUrl.js

var isValidUrl = (function() {
  var protocols = ["http", "https", "ftp"];
  var requireProtocol = false;
  var requireTLD = true;
  var pattern = new RegExp('^(?!mailto:)(?:(?:' + protocols.join('|') + ')://)' + (requireProtocol ? '' : '?') + '(?:\\S+(?::\\S*)?@)?(?:(?:(?:[1-9]\\d?|1\\d\\d|2[01]\\d|22[0-3])(?:\\.(?:1?\\d{1,2}|2[0-4]\\d|25[0-5])){2}(?:\\.(?:[0-9]\\d?|1\\d\\d|2[0-4]\\d|25[0-4]))|(?:(?:[a-z\\u00a1-\\uffff0-9]+-?)*[a-z\\u00a1-\\uffff0-9]+)(?:\\.(?:[a-z\\u00a1-\\uffff0-9]+-?)*[a-z\\u00a1-\\uffff0-9]+)*(?:\\.(?:[a-z\\u00a1-\\uffff]{2,}))' + (requireTLD ? '' : '?') + ')|localhost)(?::\\d{2,5})?(?:(/|\\?|#)[^\\s]*)?$', 'i');
  return function(str) {
    return (typeof str === "string") && str.length < 2083 && pattern.test(str);
  }
}());