is-url.js

is-url.js

/**
 * Expose `isUrl`.
 */

 module.exports = isUrl;

 /**
  * RegExps.
  * A URL must match #1 and then at least one of #2/#3.
  * Use two levels of REs to avoid REDOS.
  */
 
 var protocolAndDomainRE = /^(?:\w+:)?\/\/(\S+)$/;
 
 var localhostDomainRE = /^localhost[\:?\d]*(?:[^\:?\d]\S*)?$/
 var nonLocalhostDomainRE = /^[^\s\.]+\.\S{2,}$/;
 
 /**
  * Loosely validate a URL `string`.
  *
  * @param {String} string
  * @return {Boolean}
  */
 
 function isUrl(string){
   if (typeof string !== 'string') {
     return false;
   }
 
   var match = string.match(protocolAndDomainRE);
   if (!match) {
     return false;
   }
 
   var everythingAfterProtocol = match[1];
   if (!everythingAfterProtocol) {
     return false;
   }
 
   if (localhostDomainRE.test(everythingAfterProtocol) ||
       nonLocalhostDomainRE.test(everythingAfterProtocol)) {
     return true;
   }
 
   return false;
 }