Check if a JavaScript string is a URL_问答_开发者

Is there a way in JavaScript to check if a string is a URL?

RegExes are excluded be开发者_如何学JAVAcause the URL is most likely written like stackoverflow; that is to say that it might not have a .com, www or http.

If you want to check whether a string is valid HTTP URL, you can use URL constructor (it will throw on malformed string):

function isValidHttpUrl(string) {
  let url;
  try {
    url = new URL(string);
  } catch (_) {
    return false;
  }
  return url.protocol === "http:" || url.protocol === "https:";
}
console.log("http://example.com: "+isValidHttpUrl("https://example.com"));
console.log("example.com: "+isValidHttpUrl("example.com"));

Note: Per RFC 3886, URL must begin with a scheme (not limited to http/https), e. g.:

www.example.com is not valid URL (missing scheme)
javascript:void(0) is valid URL, although not an HTTP one
http://.. is valid URL with the host being .. (whether it resolves depends on your DNS)
https://example..com is valid URL, same as above

A related question with an answer

Or this Regexp from Devshed:

function validURL(str) {
  var pattern = new RegExp('^(https?:\\/\\/)?'+ // protocol
    '((([a-z\\d]([a-z\\d-]*[a-z\\d])*)\\.)+[a-z]{2,}|'+ // domain name
    '((\\d{1,3}\\.){3}\\d{1,3}))'+ // OR ip (v4) address
    '(\\:\\d+)?(\\/[-a-z\\d%_.~+]*)*'+ // port and path
    '(\\?[;&a-z\\d%_.~+=-]*)?'+ // query string
    '(\\#[-a-z\\d_]*)?$','i'); // fragment locator
  return !!pattern.test(str);
}

function isURL(str) {
  var pattern = new RegExp('^(https?:\\/\\/)?'+ // protocol
  '((([a-z\\d]([a-z\\d-]*[a-z\\d])*)\\.?)+[a-z]{2,}|'+ // domain name
  '((\\d{1,3}\\.){3}\\d{1,3}))'+ // OR ip (v4) address
  '(\\:\\d+)?(\\/[-a-z\\d%_.~+]*)*'+ // port and path
  '(\\?[;&a-z\\d%_.~+=-]*)?'+ // query string
  '(\\#[-a-z\\d_]*)?$','i'); // fragment locator
  return pattern.test(str);
}

Rather than using a regular expression, I would recommend making use of an anchor element.

when you set the href property of an anchor, various other properties are set.

var parser = document.createElement('a');
parser.href = "http://example.com:3000/pathname/?search=test#hash";

parser.protocol; // => "http:"
parser.hostname; // => "example.com"
parser.port;     // => "3000"
parser.pathname; // => "/pathname/"
parser.search;   // => "?search=test"
parser.hash;     // => "#hash"
parser.host;     // => "example.com:3000"

source

However, if the value href is bound to is not a valid url, then the value of those auxiliary properties will be the empty string.

Edit: as pointed out in the comments: if an invalid url is used, the properties of the current URL may be substituted.

So, as long as you're not passing in the URL of the current page, you can do something like:

function isValidURL(str) {
   var a  = document.createElement('a');
   a.href = str;
   return (a.host && a.host != window.location.host);
}

I am using below function to validate URL with or without http/https:

function isValidURL(string) {
  var res = string.match(/(http(s)?:\/\/.)?(www\.)?[-a-zA-Z0-9@:%._\+~#=]{2,256}\.[a-z]{2,6}\b([-a-zA-Z0-9@:%_\+.~#?&//=]*)/g);
  return (res !== null)
};

var testCase1 = "http://en.wikipedia.org/wiki/Procter_&_Gamble";
console.log(isValidURL(testCase1)); // return true

var testCase2 = "http://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&docid=nIv5rk2GyP3hXM&tbnid=isiOkMe3nCtexM:&ved=0CAUQjRw&url=http%3A%2F%2Fanimalcrossing.wikia.com%2Fwiki%2FLion&ei=ygZXU_2fGKbMsQTf4YLgAQ&bvm=bv.65177938,d.aWc&psig=AFQjCNEpBfKnal9kU7Zu4n7RnEt2nerN4g&ust=1398298682009707";
console.log(isValidURL(testCase2)); // return true

var testCase3 = "https://sdfasd";
console.log(isValidURL(testCase3)); // return false

var testCase4 = "dfdsfdsfdfdsfsdfs";
console.log(isValidURL(testCase4)); // return false

var testCase5 = "magnet:?xt=urn:btih:123";
console.log(isValidURL(testCase5)); // return false

var testCase6 = "https://stackoverflow.com/";
console.log(isValidURL(testCase6)); // return true

var testCase7 = "https://w";
console.log(isValidURL(testCase7)); // return false

var testCase8 = "https://sdfasdp.ppppppppppp";
console.log(isValidURL(testCase8)); // return false

To Validate Url using javascript is shown below

function ValidURL(str) {
  var regex = /(?:https?):\/\/(\w+:?\w*)?(\S+)(:\d+)?(\/|\/([\w#!:.?+=&%!\-\/]))?/;
  if(!regex .test(str)) {
    alert("Please enter valid URL.");
    return false;
  } else {
    return true;
  }
}

Rely on a library: https://www.npmjs.com/package/valid-url

import { isWebUri } from 'valid-url';
// ...
if (!isWebUri(url)) {
    return "Not a valid url.";
}

Improvement on the accepted answer...

Check for ftp/ftps as protocol
Has double escaping for backslashes (\\)
Ensures that domains have a dot and an extension (.com .io .xyz)
Allows full colon (:) in the path e.g. http://thingiverse.com/download:1894343
Allows ampersand (&) in path e.g http://en.wikipedia.org/wiki/Procter_&_Gamble

Allows @ symbol in path e.g. https://medium.com/@techytimo

isURL(str) {
  var pattern = new RegExp('^((ft|htt)ps?:\\/\\/)?'+ // protocol
  '((([a-z\\d]([a-z\\d-]*[a-z\\d])*)\\.)+[a-z]{2,}|'+ // domain name and extension
  '((\\d{1,3}\\.){3}\\d{1,3}))'+ // OR ip (v4) address
  '(\\:\\d+)?'+ // port
  '(\\/[-a-z\\d%@_.~+&:]*)*'+ // path
  '(\\?[;&a-z\\d%@_.,~+&:=-]*)?'+ // query string
  '(\\#[-a-z\\d_]*)?$','i'); // fragment locator
  return pattern.test(str);
}

You can use the URL native API:

  const isUrl = string => {
      try { return Boolean(new URL(string)); }
      catch(e){ return false; }
  }

Use validator.js

ES6

import isURL from 'validator/lib/isURL'

isURL(string)

No ES6

var validator = require('validator');

validator.isURL(string)

You can also fine tune this function's behavior by passing optional options object as the second argument of isURL

Here is the default options object:

let options = {
    protocols: [
        'http',
        'https',
        'ftp'
    ],
    require_tld: true,
    require_protocol: false,
    require_host: true,
    require_valid_protocol: true,
    allow_underscores: false,
    host_whitelist: false,
    host_blacklist: false,
    allow_trailing_dot: false,
    allow_protocol_relative_urls: false,
    disallow_auth: false
}

isURL(string, options)

host_whitelist and host_blacklist can be arrays of hosts. They also support regular expressions.

let options = {
    host_blacklist: ['foo.com', 'bar.com'],
}

isURL('http://foobar.com', options) // => true
isURL('http://foo.bar.com/', options) // => true
isURL('http://qux.com', options) // => true

isURL('http://bar.com/', options) // => false
isURL('http://foo.com/', options) // => false


options = {
    host_blacklist: ['bar.com', 'foo.com', /\.foo\.com$/],
}

isURL('http://foobar.com', options) // => true
isURL('http://foo.bar.com/', options) // => true
isURL('http://qux.com', options) // => true

isURL('http://bar.com/', options) // => false
isURL('http://foo.com/', options) // => false
isURL('http://images.foo.com/', options) // => false
isURL('http://cdn.foo.com/', options) // => false
isURL('http://a.b.c.foo.com/', options) // => false

Here is yet another method.

// ***note***: if the incoming value is empty(""), the function returns true

var elm;
function isValidURL(u){
  //A precaution/solution for the problem written in the ***note***
  if(u!==""){  
      if(!elm){
      elm = document.createElement('input');
      elm.setAttribute('type', 'url');
      }
  elm.value = u;
  return elm.validity.valid;
  }
  else{
      return false
  }
}

console.log(isValidURL(''));
console.log(isValidURL('http://www.google.com/'));
console.log(isValidURL('//google.com'));
console.log(isValidURL('google.com'));
console.log(isValidURL('localhost:8000'));

As has been noted the perfect regex is elusive but still seems to be a reasonable approach (alternatives are server side tests or the new experimental URL API). However the high ranking answers are often returning false for common URLs but even worse will freeze your app/page for minutes on even as simple a string as isURL('aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa'). It's been pointed out in some of the comments, but most probably haven't entered a bad value to see it. Hanging like that makes that code unusable in any serious application. I think it's due to the repeated case insensitive sets in code like ((([a-z\\d]([a-z\\d-]*[a-z\\d])*)\\.?)+[a-z]{2,}|' .... Take out the 'i' and it doesn't hang but will of course not work as desired. But even with the ignore case flag those tests reject high unicode values that are allowed.

The best already mentioned is:

function isURL(str) {
  return /^(?:\w+:)?\/\/([^\s\.]+\.\S{2}|localhost[\:?\d]*)\S*$/.test(str); 
}

That comes from Github segmentio/is-url. The good thing about a code repository is you can see the testing and any issues and also the test strings run through it. There's a branch that would allow strings missing protocol like google.com, though you're probably making too many assumptions then. The repository has been updated and I'm not planning on trying to keep up a mirror here. It's been broken up into separate tests to avoid RegEx redos which can be exploited for DOS attacks (I don't think you have to worry about that with client side js, but you do have to worry about your page hanging for so long that your visitor leaves your site).

There is one other repository I've seen that may even be better for isURL at dperini/regex-weburl.js, but it is highly complex. It has a bigger test list of valid and invalid URLs. The simple one above still passes all the positives and only fails to block a few odd negatives like http://a.b--c.de/ as well as the special ips.

Whichever you choose, run it through this function which I've adapted from the tests on dperini/regex-weburl.js, while using your browser's Developer Tools inpector.

function testIsURL() {
//should match
console.assert(isURL("http://foo.com/blah_blah"));
console.assert(isURL("http://foo.com/blah_blah/"));
console.assert(isURL("http://foo.com/blah_blah_(wikipedia)"));
console.assert(isURL("http://foo.com/blah_blah_(wikipedia)_(again)"));
console.assert(isURL("http://www.example.com/wpstyle/?p=364"));
console.assert(isURL("https://www.example.com/foo/?bar=baz&inga=42&quux"));
console.assert(isURL("http://✪df.ws/123"));
console.assert(isURL("http://userid:password@example.com:8080"));
console.assert(isURL("http://userid:password@example.com:8080/"));
console.assert(isURL("http://userid@example.com"));
console.assert(isURL("http://userid@example.com/"));
console.assert(isURL("http://userid@example.com:8080"));
console.assert(isURL("http://userid@example.com:8080/"));
console.assert(isURL("http://userid:password@example.com"));
console.assert(isURL("http://userid:password@example.com/"));
console.assert(isURL("http://142.42.1.1/"));
console.assert(isURL("http://142.42.1.1:8080/"));
console.assert(isURL("http://➡.ws/䨹"));
console.assert(isURL("http://⌘.ws"));
console.assert(isURL("http://⌘.ws/"));
console.assert(isURL("http://foo.com/blah_(wikipedia)#cite-1"));
console.assert(isURL("http://foo.com/blah_(wikipedia)_blah#cite-1"));
console.assert(isURL("http://foo.com/unicode_(✪)_in_parens"));
console.assert(isURL("http://foo.com/(something)?after=parens"));
console.assert(isURL("http://☺.damowmow.com/"));
console.assert(isURL("http://code.google.com/events/#&product=browser"));
console.assert(isURL("http://j.mp"));
console.assert(isURL("ftp://foo.bar/baz"));
console.assert(isURL("http://foo.bar/?q=Test%20URL-encoded%20stuff"));
console.assert(isURL("http://مثال.إختبار"));
console.assert(isURL("http://例子.测试"));
console.assert(isURL("http://उदाहरण.परीक्षा"));
console.assert(isURL("http://-.~_!$&'()*+,;=:%40:80%2f::::::@example.com"));
console.assert(isURL("http://1337.net"));
console.assert(isURL("http://a.b-c.de"));
console.assert(isURL("http://223.255.255.254"));
console.assert(isURL("postgres://u:p@example.com:5702/db"));
console.assert(isURL("https://d1f4470da51b49289906b3d6cbd65074@app.getsentry.com/13176"));

//SHOULD NOT MATCH:
console.assert(!isURL("http://"));
console.assert(!isURL("http://."));
console.assert(!isURL("http://.."));
console.assert(!isURL("http://../"));
console.assert(!isURL("http://?"));
console.assert(!isURL("http://??"));
console.assert(!isURL("http://??/"));
console.assert(!isURL("http://#"));
console.assert(!isURL("http://##"));
console.assert(!isURL("http://##/"));
console.assert(!isURL("http://foo.bar?q=Spaces should be encoded"));
console.assert(!isURL("//"));
console.assert(!isURL("//a"));
console.assert(!isURL("///a"));
console.assert(!isURL("///"));
console.assert(!isURL("http:///a"));
console.assert(!isURL("foo.com"));
console.assert(!isURL("rdar://1234"));
console.assert(!isURL("h://test"));
console.assert(!isURL("http:// shouldfail.com"));
console.assert(!isURL(":// should fail"));
console.assert(!isURL("http://foo.bar/foo(bar)baz quux"));
console.assert(!isURL("ftps://foo.bar/"));
console.assert(!isURL("http://-error-.invalid/"));
console.assert(!isURL("http://a.b--c.de/"));
console.assert(!isURL("http://-a.b.co"));
console.assert(!isURL("http://a.b-.co"));
console.assert(!isURL("http://0.0.0.0"));
console.assert(!isURL("http://10.1.1.0"));
console.assert(!isURL("http://10.1.1.255"));
console.assert(!isURL("http://224.1.1.1"));
console.assert(!isURL("http://1.1.1.1.1"));
console.assert(!isURL("http://123.123.123"));
console.assert(!isURL("http://3628126748"));
console.assert(!isURL("http://.www.foo.bar/"));
console.assert(!isURL("http://www.foo.bar./"));
console.assert(!isURL("http://.www.foo.bar./"));
console.assert(!isURL("http://10.1.1.1"));}

And then test that string of 'a's.

See this comparison of isURL regex by Mathias Bynens for more info before you post a seemingly great regex.

This function disallows localhost and only allows URLs for web pages (ie, only allows http or https protocol).

It also only allows safe characters as defined here: https://www.urlencoder.io/learn/

function isValidWebUrl(url) {
   let regEx = /^https?:\/\/(?:www\.)?[-a-zA-Z0-9@:%._\+~#=]{1,256}\.[a-zA-Z0-9()]{1,6}\b([-a-zA-Z0-9()@:%_\+.~#?&//=]*)$/gm;
   return regEx.test(url);
}

(I don't have reps to comment on ValidURL example; hence post this as an answer.)

While use of protocol relative URLs is not encouraged (The Protocol-relative URL), they do get employed sometimes. To validate such an URL with a regular expression the protocol part could be optional, e.g.:

function isValidURL(str) {
    var pattern = new RegExp('^((https?:)?\\/\\/)?'+ // protocol
        '(?:\\S+(?::\\S*)?@)?' + // authentication
        '((([a-z\\d]([a-z\\d-]*[a-z\\d])*)\\.)+[a-z]{2,}|'+ // domain name
        '((\\d{1,3}\\.){3}\\d{1,3}))'+ // OR ip (v4) address
        '(\\:\\d+)?(\\/[-a-z\\d%_.~+]*)*'+ // port and path
        '(\\?[;&a-z\\d%_.~+=-]*)?'+ // query string
        '(\\#[-a-z\\d_]*)?$','i'); // fragment locater
    if (!pattern.test(str)) {
        return false;
    } else {
        return true;
    }
}

As others noted, regular expression does not seem to be the best suited approach for validating URLs, though.

One function that I have been using to validate a URL "string" is:

var matcher = /^(?:\w+:)?\/\/([^\s\.]+\.\S{2}|localhost[\:?\d]*)\S*$/;

function isUrl(string){
  return matcher.test(string);
}

This function will return a boolean whether the string is a URL.

Examples:

isUrl("https://google.com");     // true
isUrl("http://google.com");      // true
isUrl("http://google.de");       // true
isUrl("//google.de");            // true
isUrl("google.de");              // false
isUrl("http://google.com");      // true
isUrl("http://localhost");       // true
isUrl("https://sdfasd");         // false

I can't comment on the post that is the closest #5717133, but below is the way I figured out how to get @tom-gullen regex working.

/^(https?:\/\/)?((([a-z\d]([a-z\d-]*[a-z\d])*)\.)+[a-z]{2,}|((\d{1,3}\.){3}\d{1,3}))(\:\d+)?(\/[-a-z\d%_.~+]*)*(\?[;&a-z\d%_.~+=-]*)?(\#[-a-z\d_]*)?$/i

There's a lot of answers already, but here's another contribution: Taken directly from the URL polyfill validity check, use an input element with type="url" to take advantage of the browser's built-in validity check:

var inputElement = doc.createElement('input');
inputElement.type = 'url';
inputElement.value = url;

if (!inputElement.checkValidity()) {
    throw new TypeError('Invalid URL');
}

Source

This is quite difficult to do with pure regex because URLs have many 'inconveniences'.

For example domain names have complicated restrictions on hyphens:

a. It is allowed to have many consecutive hyphens in the middle.

b. but the first character and last character of the domain name cannot be a hyphen

c. The 3rd and 4th character cannot be both hyphen
Similarly port number can only be in the range 1-65535. This is easy to check if you extract the port part and convert to int but quite difficult to check with a regular expression.
There is also no easy way to check valid domain extensions. Some countries have second-level domains(such as 'co.uk'), or the extension can be a long word such as '.international'. And new TLDs are added regularly. This type of things can only be checked against a hard-coded list. (see https://en.wikipedia.org/wiki/Top-level_domain)
Then there are magnet urls, ftp addresses etc. These all have different requirements.

Nevertheless, here is a function that handles pretty much everything except:

Case 1. c
Accepts any 1-5 digit port number
Accepts any extension 2-13 chars
Does not accept ftp, magnet, etc...

function isValidURL(input) {
    pattern = '^(https?:\\/\\/)?' + // protocol
        '((([a-zA-Z\\d]([a-zA-Z\\d-]{0,61}[a-zA-Z\\d])*\\.)+' + // sub-domain + domain name
        '[a-zA-Z]{2,13})' + // extension
        '|((\\d{1,3}\\.){3}\\d{1,3})' + // OR ip (v4) address
        '|localhost)' + // OR localhost
        '(\\:\\d{1,5})?' + // port
        '(\\/[a-zA-Z\\&\\d%_.~+-:@]*)*' + // path
        '(\\?[a-zA-Z\\&\\d%_.,~+-:@=;&]*)?' + // query string
        '(\\#[-a-zA-Z&\\d_]*)?$'; // fragment locator
    regex = new RegExp(pattern);
    return regex.test(input);
}

let tests = [];
tests.push(['', false]);
tests.push(['http://en.wikipedia.org/wiki/Procter_&_Gamble', true]);
tests.push(['https://sdfasd', false]);
tests.push(['http://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&docid=nIv5rk2GyP3hXM&tbnid=isiOkMe3nCtexM:&ved=0CAUQjRw&url=http%3A%2F%2Fanimalcrossing.wikia.com%2Fwiki%2FLion&ei=ygZXU_2fGKbMsQTf4YLgAQ&bvm=bv.65177938,d.aWc&psig=AFQjCNEpBfKnal9kU7Zu4n7RnEt2nerN4g&ust=1398298682009707', true]);
tests.push(['https://stackoverflow.com/', true]);
tests.push(['https://w', false]);
tests.push(['aaa', false]);
tests.push(['aaaa', false]);
tests.push(['oh.my', true]);
tests.push(['dfdsfdsfdfdsfsdfs', false]);
tests.push(['google.co.uk', true]);
tests.push(['test-domain.MUSEUM', true]);
tests.push(['-hyphen-start.gov.tr', false]);
tests.push(['hyphen-end-.com', false]);
tests.push(['https://sdfasdp.international', true]);
tests.push(['https://sdfasdp.pppppppp', false]);
tests.push(['https://sdfasdp.ppppppppppppppppppp', false]);
tests.push(['https://sdfasd', false]);
tests.push(['https://sub1.1234.sub3.sub4.sub5.co.uk/?', true]);
tests.push(['http://www.google-com.123', false]);
tests.push(['http://my--testdomain.com', false]);
tests.push(['http://my2nd--testdomain.com', true]);
tests.push(['http://thingiverse.com/download:1894343', true]);
tests.push(['https://medium.com/@techytimo', true]);
tests.push(['http://localhost', true]);
tests.push(['localhost', true]);
tests.push(['localhost:8080', true]);
tests.push(['localhost:65536', true]);
tests.push(['localhost:80000', false]);
tests.push(['magnet:?xt=urn:btih:123', true]);

for (let i = 0; i < tests.length; i++) {
    console.log('Test #' + i + (isValidURL(tests[i][0]) == tests[i][1] ? ' passed' : ' failed') + ' on ["' + tests[i][0] + '", ' + tests[i][1] + ']');
}

Mathias Bynens has compiled a list of well-known URL regexes with test URLs. There is little reason to write a new regular expression; just pick an existing one that suits you best.

But the comparison table for those regexes also shows that it is next to impossible to do URL validation with a single regular expression. All of the regexes in Bynens' list produce false positives and false negatives.

I suggest that you use an existing URL parser (for example new URL('http://www.example.com/') in JavaScript) and then apply the checks you want to perform against the parsed and normalized form of the URL resp. its components. Using the JavaScript URL interface has the additional benefit that it will only accept such URLs that are really accepted by the browser.

You should also keep in mind that technically incorrect URLs may still work. For example http://w_w_w.example.com/, http://www..example.com/, http://123.example.com/ all have an invalid hostname part but every browser I know will try to open them without complaints, and when you specify IP addresses for those invalid names in /etc/hosts/ such URLs will even work but only on your computer.

The question is, therefore, not so much whether a URL is valid, but rather which URLs work and should be allowed in a particular context.

If you want to do URL validation there are a lot of details and edge cases that are easy to overlook:

URLs may contain credentials as in http://user:password@www.example.com/.
Port numbers must be in the range of 0-65535, but you may still want to exclude the wildcard port 0.
Port numbers may have leading zeros as in http://www.example.com:000080/.
IPv4 addresses are by no means restricted to 4 decimal integers in the range of 0-255. You can use one to four integers, and they can be decimal, octal or hexadecimal. The URLs https://010.010.000010.010/, https://0x8.0x8.0x0008.0x8/, https://8.8.2056/, https://8.526344/, https://134744072/ are all valid and just creative ways of writing https://8.8.8.8/.
Allowing loopback addresses (http://127.0.0.1/), private IP addresses (http://192.168.1.1), link-local addresses (http://169.254.100.200) and so on may have an impact on security or privacy. If, for instance, you allow them as the address of user avatars in a forum, you cause the users' browsers to send unsolicited network requests in their local network and in the internet of things such requests may cause funny and not so funny things to happen in your home.
For the same reasons, you may want to discard links to not fully qualified hostnames, in other words hostnames without a dot.
But hostnames may always have a trailing dot (like in http://www.stackoverflow.com.).
The hostname portion of a link may contain angle brackets for IPv6 addresses as in http://[::1].
IPv6 addresses also have ranges for private networks or link-local addresses etc.
If you block certain IPv4 addresses, keep in mind that for example https://127.0.0.1 and https://[::ffff:127.0.0.1] point to the same resource (if the loopback device of your machine is IPv6 ready).
The hostname portion of URLs may now contain Unicode, so that the character range [-0-9a-zA-z] is definitely no longer sufficient.
Many registries for top-level domains define specific restrictions, for example on the allowed set of Unicode characters. Or they subdivide their namespace (like co.uk and many others).
Top-level domains must not contain decimal digits, and the hyphen is not allowed unless for the IDN A-label prefix "xn--".
Unicode top-level domains (and their punycode encoding with "xn--") must still contain only letters but who wants to check that in a regex?

Which of these limitations and rules apply is a question of project requirements and taste.

I have recently written a URL validator for a web app that is suitable for user-supplied URLs in forums, social networks, or the like. Feel free to use it as a base for your own one:

JavaScript/Typescript version for the (Angular) frontend
Perl version for the backend

I have also written a blog post The Gory Details of URL Validation with more in-depth information.

this working with me

function isURL(str) {
  var regex = /(http|https):\/\/(\w+:{0,1}\w*)?(\S+)(:[0-9]+)?(\/|\/([\w#!:.?+=&%!\-\/]))?/;
  var pattern = new RegExp(regex); 
return pattern.test(str);
}

There are a couple of tests using the URL constructor which do not delineate whether the input is a string or URL object.

// Testing whether something is a URL
function isURL(url) {
    return toString.call(url) === "[object URL]";
}

// Testing whether the input is both a string and valid url:
function isUrl(url) {
    try {
        return toString.call(url) === "[object String]" && !!(new URL(url));
    } catch (_) {
        return false;  
    }
}

I had revised all the comments, notes and remarks is this topic and have made a new regular expression:

^((javascript:[\w-_]+(\([\w-_\s,.]*\))?)|(mailto:([\w\u00C0-\u1FFF\u2C00-\uD7FF-_]+\.)*[\w\u00C0-\u1FFF\u2C00-\uD7FF-_]+@([\w\u00C0-\u1FFF\u2C00-\uD7FF-_]+\.)*[\w\u00C0-\u1FFF\u2C00-\uD7FF-_]+)|(\w+:\/\/(([\w\u00C0-\u1FFF\u2C00-\uD7FF-]+\.)*([\w\u00C0-\u1FFF\u2C00-\uD7FF-]*\.?))(:\d+)?(((\/[^\s#$%^&*?]+)+|\/)(\?[\w\u00C0-\u1FFF\u2C00-\uD7FF:;&%_,.~+=-]+)?)?(#[\w\u00C0-\u1FFF\u2C00-\uD7FF-_]+)?))$

You can test and improve it here https://regexr.com/668mt .

I checked this expression on next values:

http://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&docid=nIv5rk2GyP3hXM&tbnid=isiOkMe3nCtexM:&ved=0CAUQjRw&url=http%3A%2F%2Fanimalcrossing.wikia.com%2Fwiki%2FLion&ei=ygZXU_2fGKbMsQTf4YLgAQ&bvm=bv.65177938,d.aWc&psig=AFQjCNEpBfKnal9kU7Zu4n7RnEt2nerN4g&ust=1398298682009707
http://192.168.0.4:55/
https://web.archive.org/web/20170817095211/https://github.com/Microsoft/vscode/issues/32405
http://www.example.com
javascript:void()
http://.
https://example.
https://en.m.wikipedia.org/wiki/C_Sharp_(programming_language)
http://zh.wikipedia.org/wiki/Wikipedia:关于中文维基百科/en?a#a
https://medium.com/@User_name/
https://test-test-test-test-test-test-test-test-test.web.app/
http://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&docid=nIv5rk2GyP3hXM&tbnid=isiOkMe3nCtexM:&ved=0CAUQjRw&url=http%3A%2F%2Fanimalcrossing.wikia.com%2Fwiki%2FLion&ei=ygZXU_2fGKbMsQTf4YLgAQ&bvm=bv.65177938,d.aWc&psig=AFQjCNEpBfKnal9kU7Zu4n7RnEt2nerN4g&ust=1398298682009707
https://sdfasdp.ppppppppppp
mailto:sadf@gmail.com
https://тест.юа

If you can change the input type, I think this solution would be much easier:

You can simple use type="url" in your input and the check it with checkValidity() in js

E.g:

your.html

<input id="foo" type="url">

your.js

// The selector is JQuery, but the function is plain JS
$("#foo").on("keyup", function() {
    if (this.checkValidity()) {
        // The url is valid
    } else {
        // The url is invalid
    }
});

If you need to also support https://localhost:3000 then use this modified version of [Devshed]s regex.

    function isURL(url) {
        if(!url) return false;
        var pattern = new RegExp('^(https?:\\/\\/)?'+ // protocol
            '((([a-z\\d]([a-z\\d-]*[a-z\\d])*)\\.)+[a-z]{2,}|'+ // domain name
            '((\\d{1,3}\\.){3}\\d{1,3}))|' + // OR ip (v4) address
            'localhost' + // OR localhost
            '(\\:\\d+)?(\\/[-a-z\\d%_.~+]*)*'+ // port and path
            '(\\?[;&a-z\\d%_.~+=-]*)?'+ // query string
            '(\\#[-a-z\\d_]*)?$', 'i'); // fragment locator
        return pattern.test(url);
    }

I change the function to Match + make a change here with the slashes and its work: (http:// and https) both

function isValidUrl(userInput) {
    var res = userInput.match(/(http(s)?:\/\/.)?(www\.)?[-a-zA-Z0-9@:%._\+~#=]{2,256}\.[a-z]{2,6}\b([-a-zA-Z0-9@:%_\+.~#?&//=]*)/g);
    if(res == null)
       return false;
    else
       return true;
}

I think using the native URL API is better than a complex regex patterns as @pavlo suggested. It has some drawbacks though which we can fix by some extra code. This approach fails for the following valid url.

//cdn.google.com/script.js

We can add the missing protocol beforehand to avoid that. It also fails to detect following invalid url.

http://w
http://..

So why check the whole url? we can just check the domain. I borrowed the regex to verify domain from here.

function isValidUrl(string) {
    if (string && string.length > 1 && string.slice(0, 2) == '//') {
        string = 'http:' + string; //dummy protocol so that URL works
    }
    try {
        var url = new URL(string);
        return url.hostname && url.hostname.match(/^([a-z0-9])(([a-z0-9-]{1,61})?[a-z0-9]{1})?(\.[a-z0-9](([a-z0-9-]{1,61})?[a-z0-9]{1})?)?(\.[a-zA-Z]{2,4})+$/) ? true : false;
    } catch (_) {
        return false;
    }
}

The hostname attribute is empty string for javascript:void(0), so it works for that too, and you can also add IP address verifier too. I'd like to stick to native API's most, and hope it starts to support everything in near future.

The question asks a validation method for an url such as stackoverflow, without the protocol or any dot in the hostname. So, it's not a matter of validating url sintax, but checking if it's a valid url, by actually calling it.

I tried several methods for knowing if the url true exists and is callable from within the browser, but did not find any way to test with javascript the response header of the call:

adding an anchor element is fine for firing the click() method.
making ajax call to the challenging url with 'GET' is fine, but has it's various limitations due to CORS policies and it is not the case of using ajax, for as the url maybe any outside my server's domain.
using the fetch API has a workaround similar to ajax.
other problem is that I have my server under https protocol and throws an exception when calling non secure urls.

So, the best solution I can think of is getting some tool to perform CURL using javascript trying something like curl -I <url>. Unfortunately I did not find any and in appereance it's not possible. I will appreciate any comments on this.

But, in the end, I have a server running PHP and as I use Ajax for almost all my requests, I wrote a function on the server side to perform the curl request there and return to the browser.

Regarding the single word url on the question 'stackoverflow' it will lead me to https://daniserver.com.ar/stackoverflow, where daniserver.com.ar is my own domain.

This seems to be one of the hardest problems in CS ;)

Here's another incomplete solution that works well enough for me and better than the others I've seen here. I'm using a input[type=url] for this in order to support IE11, otherwise it would be much simpler using window.URL to perform the validation instead:

const ipv4Regex = /^(\d{1,3}\.){3}\d{1,3}$/;
function isValidIpv4(ip) {
  if (!ipv4Regex.test(ip)) return false;
  return !ip.split('.').find(n => n > 255);
}

const domainRegex = /(?:[a-z0-9-]{1,63}\.){1,125}[a-z]{2,63}$/i;
function isValidDomain(domain) {
  return isValidIpv4(domain) || domainRegex.test(domain);
}

let input;
function validateUrl(url) {
  if (! /^https?:\/\//.test(url)) url = `http://${url}`; // assuming Babel is used
  // to support IE11 we'll resort to input[type=url] instead of window.URL:
  // try { return isValidDomain(new URL(url).host) && url; } catch(e) { return false; }
  if (!input) { input = document.createElement('input'); input.type = 'url'; }
  input.value = url;
  if (! input.validity.valid) return false;
  const domain = url.split(/^https?:\/\//)[1].split('/')[0].split('@').pop();
  return isValidDomain(domain) && url;
}

console.log(validateUrl('google'), // false
  validateUrl('user:pw@mydomain.com'),
  validateUrl('https://google.com'),
  validateUrl('100.100.100.100/abc'),
  validateUrl('100.100.100.256/abc')); // false

In order to accept incomplete inputs such as "www.mydomain.com" it will also make it valid assuming the protocol is "http" in those cases and returning the valid URL if the address is valid. It returns false when invalid.

It also supports IPv4 domains, but not IPv6.

In my case my only requirement is that the user input won't be interpreted as a relative link when placed in the href of an a tag and the answers here were either a bit OTT for that or allowed URLs not meeting my requirements, so this is what I'm going with:

^https?://.+$

The same thing could be achieved pretty easily without regex.

This is defiantly not the most effective approach, but it is readable and easy to form to whatever you need. And it's easier to add regex/complexity from here. So here is a very pragmatic approach

const validFirstBits = ["ftp://", "http://", "https://", "www."];
const invalidPatterns = [" ", "//.", ".."];

export function isUrl(word) {
// less than www.1.dk
if (!word || word.length < 8) return false;

// Let's check and see, if our candidate starts with some of our valid first bits
const firstBitIsValid = validFirstBits.some(bit => word.indexOf(bit) === 0);
if (!firstBitIsValid) return false;

const hasInvalidPatterns = invalidPatterns.some(
    pattern => word.indexOf(pattern) !== -1,
);

if (hasInvalidPatterns) return false;

const dotSplit = word.split(".");
if (dotSplit.length > 1) {
    const lastBit = dotSplit.pop(); // string or undefined
    if (!lastBit) return false;
    const length = lastBit.length;
    const lastBitIsValid =
        length > 1 || (length === 1 && !isNaN(parseInt(lastBit)));
    return !!lastBitIsValid;
}

    return false;
}

TEST:

import { isUrl } from "./foo";

describe("Foo", () => {
    test("should validate correct urls correctly", function() {
        const validUrls = [
            "http://example.com",
            "http://example.com/blah",
            "http://127.0.0.1",
            "http://127.0.0.1/wow",
            "https://example.com",
            "https://example.com/blah",
            "https://127.0.0.1:1234",
            "ftp://example.com",
            "ftp://example.com/blah",
            "ftp://127.0.0.1",
            "www.example.com",
            "www.example.com/blah",
        ];

        validUrls.forEach(url => {
            expect(isUrl(url) && url).toEqual(url);
        });
    });

    test("should validate invalid urls correctly", function() {
        const inValidUrls = [
            "http:// foo.com",
            "http:/foo.com",
            "http://.foo.com",
            "http://foo..com",
            "http://.com",
            "http://foo",
            "http://foo.c",
        ];

        inValidUrls.forEach(url => {
            expect(!isUrl(url) && url).toEqual(url);
        });
    });
});