How to detect whether a string is in URL format using javascript?

One for the future using the URL constructor and a basic try catch statement, it is supported in most modern browsers. Obviously no IE support...

const isUrl = (str) => {
  try {
    new URL(str);
    return true;
  } catch () {
    return false;  
  }
}

If the URL is valid it will get parsed by the constructor and return true.

If the string is not a valid URL the constructor will chuck a syntax error that will get caught and return false.

function IsURL(url) {

    var strRegex = "^((https|http|ftp|rtsp|mms)?://)"
        + "?(([0-9a-z_!~*'().&=+$%-]+: )?[0-9a-z_!~*'().&=+$%-]+@)?" //ftp的user@
        + "(([0-9]{1,3}\.){3}[0-9]{1,3}" // IP形式的URL- 199.194.52.184
        + "|" // 允许IP和DOMAIN（域名）
        + "([0-9a-z_!~*'()-]+\.)*" // 域名- www.
        + "([0-9a-z][0-9a-z-]{0,61})?[0-9a-z]\." // 二级域名
        + "[a-z]{2,6})" // first level domain- .com or .museum
        + "(:[0-9]{1,4})?" // 端口- :80
        + "((/?)|" // a slash isn't required if there is no file name
        + "(/[0-9a-z_!~*'().;?:@&=+$,%#-]+)+/?)$";
     var re=new RegExp(strRegex);
     return re.test(url);
 }

Debuggex Demo (Improved version which matches also 'localhost')

try something like this:

function isUrl(s) {
    var regexp = /(ftp|http|https):\/\/(\w+:{0,1}\w*@)?(\S+)(:[0-9]+)? (\/|\/([\w#!:.?+=&%@!\-\/]))?/
    return regexp.test(s);
}

Try this-

function isUrl(s) {
   var regexp = /(ftp|http|https):\/\/(\w+:{0,1}\w*@)?(\S+)(:[0-9]+)?(\/|\/([\w#!:.?+=&%@!\-\/]))?/
   return regexp.test(s);
}

usage: if (isUrl("http://www.page.com")) alert("is correct") else alert("not correct");