Can I perform a DNS lookup (hostname to IP address) using client-side Javascript?

Question

I would like to use client-side Javascript to perform a DNS lookup (hostname to IP address) as seen from the client's computer. Is that possible?

Answer 1

Edit: This question gave me an itch, so I put up a JSONP webservice on Google App Engine that returns the clients ip address. Usage:

<script type="application/javascript">
function getip(json){
  alert(json.ip); // alerts the ip address
}
</script>

<script type="application/javascript" src="http://jsonip.appspot.com/?callback=getip"> </script>

Yay, no server proxies needed.

---

Pure JS can't. If you have a server script under the same domain that prints it out you could send a XMLHttpRequest to read it.

Answer 2

There's no notion of hosts or ip-addresses in the javascript standard library. So you'll have to access some external service to look up hostnames for you.

I recommend hosting a cgi-bin which looks up the ip-address of a hostname and access that via javascript.

Answer 3

Very late, but I guess many people will still land here through "Google Airlines". A moderm approach is to use WebRTC that doesn't require server support.

https://hacking.ventures/local-ip-discovery-with-html5-webrtc-security-and-privacy-risk/

Next code is a copy&paste from http://net.ipcalf.com/

// NOTE: window.RTCPeerConnection is "not a constructor" in FF22/23
var RTCPeerConnection = /*window.RTCPeerConnection ||*/ window.webkitRTCPeerConnection || window.mozRTCPeerConnection;

if (RTCPeerConnection) (function () {
    var rtc = new RTCPeerConnection({iceServers:[]});
    if (window.mozRTCPeerConnection) {      // FF needs a channel/stream to proceed
        rtc.createDataChannel('', {reliable:false});
    };  

    rtc.onicecandidate = function (evt) {
        if (evt.candidate) grepSDP(evt.candidate.candidate);
    };  
    rtc.createOffer(function (offerDesc) {
        grepSDP(offerDesc.sdp);
        rtc.setLocalDescription(offerDesc);
    }, function (e) { console.warn("offer failed", e); }); 


    var addrs = Object.create(null);
    addrs["0.0.0.0"] = false;
    function updateDisplay(newAddr) {
        if (newAddr in addrs) return;
        else addrs[newAddr] = true;
        var displayAddrs = Object.keys(addrs).filter(function (k) { return addrs[k]; }); 
        document.getElementById('list').textContent = displayAddrs.join(" or perhaps ") || "n/a";
    }   

    function grepSDP(sdp) {
        var hosts = []; 
        sdp.split('\r\n').forEach(function (line) { // c.f. http://tools.ietf.org/html/rfc4566#page-39
            if (~line.indexOf("a=candidate")) {     // http://tools.ietf.org/html/rfc4566#section-5.13
                var parts = line.split(' '),        // http://tools.ietf.org/html/rfc5245#section-15.1
                    addr = parts[4],
                    type = parts[7];
                if (type === 'host') updateDisplay(addr);
            } else if (~line.indexOf("c=")) {       // http://tools.ietf.org/html/rfc4566#section-5.7
                var parts = line.split(' '), 
                    addr = parts[2];
                updateDisplay(addr);
            }   
        }); 
    }   
})(); else {
    document.getElementById('list').innerHTML = "<code>ifconfig | grep inet | grep -v inet6 | cut -d\" \" -f2 | tail -n1</code>";
    document.getElementById('list').nextSibling.textContent = "In Chrome and Firefox your IP should display automatically, by the power of WebRTCskull.";
}   

Answer 4

I know this question was asked a very long time ago, but I figured I'd offer a more recent answer.

DNS over HTTPS (DoH)

You can send DNS queries over HTTPS to DNS resolvers that support it. The standard for DOH is described in RFC 8484.

This is a similar thing to what all the other answers suggest, only that DoH is actually the DNS protocol over HTTPS. It's also a "proposed" Internet standard and it's becoming quite popular. For example, some major browsers either support it or have plans to support it (Chrome, Edge, Firefox), and Microsoft is in the process of building it into their operating system.

One of the purposes of DoH is:

allowing web applications to access DNS information via existing browser APIs in a safe way consistent with Cross Origin Resource Sharing (CORS)

There's an open source tool made especially for doing DNS lookups from web applications called dohjs. It does DNS over HTTPS (DoH) wireformat queries as described in RFC 8484. It supports both GET and POST methods.

Full disclosure: I am a contributor to dohjs.

Another JavaScript library with similar features is found here - https://github.com/sc0Vu/doh-js-client. I haven't used this one personally, but I think it would work client side as well.

DNS over HTTPS JSON APIs

If you don't want to bother with DNS wireformat, both Google and Cloudflare offer JSON APIs for DNS over HTTPS.

• Google's endpoint: https://dns.google/resolve?
• Google's JSON API docs: https://developers.google.com/speed/public-dns/docs/doh/json
• Cloudflare's endpoint: https://cloudflare-dns.com/dns-query?
• Cloudflare's JSON API docs: https://developers.cloudflare.com/1.1.1.1/dns-over-https/json-format/

Example Javascript code to lookup example.com with Google's JSON DOH API:

var response = await fetch('https://dns.google/resolve?name=example.com');
var json = await response.json();
console.log(json);

Examples from the RFC for DOH GET and POST with wireformat

Here are the examples the RFC gives for both GET and POST (see https://tools.ietf.org/html/rfc8484#section-4.1.1):

GET example:

The first example request uses GET to request "www.example.com".

:method = GET
:scheme = https
:authority = dnsserver.example.net
:path = /dns-query?dns=AAABAAABAAAAAAAAA3d3dwdleGFtcGxlA2NvbQAAAQAB
accept = application/dns-message

POST example:

The same DNS query for "www.example.com", using the POST method would be:

:method = POST
:scheme = https
:authority = dnsserver.example.net
:path = /dns-query
accept = application/dns-message
content-type = application/dns-message
content-length = 33

<33 bytes represented by the following hex encoding> 00 00 01 00 00 01 00 00 00 00 00 00 03 77 77 77 07 65 78 61 6d 70 6c 65 03 63 6f 6d 00 00 01 00 01

Other places to send DOH queries

You can find a list of some public DNS resolvers that support DNS over HTTPS in a couple places:

• DNSCrypt has a long list of public DoH and DNSCrypt resolver on their Github, and a nice interactive version of the list at https://dnscrypt.info/public-servers/
• Wikipedia - comparison of public recursive nameservers
• List on Curl's wiki
• (short) list on dnsprivacy.org

Of the above resources, I'd say that the list on Curl's wiki and the DNSCrypt list are are probably the most complete and the most frequently updated. Curl's page also includes a list of open source tools for DoH (servers, proxies, client libs, etc).

Answer 5

The hosted JSONP version works like a charm, but it seems it goes over its resources during night time most days (Eastern Time), so I had to create my own version.

This is how I accomplished it with PHP:

<?php
header('content-type: application/json; charset=utf-8');

$data = json_encode($_SERVER['REMOTE_ADDR']);
echo $_GET['callback'] . '(' . $data . ');';
?>

Then the Javascript is exactly the same as before, just not an array:

<script type="application/javascript">
function getip(ip){
    alert('IP Address: ' + ip);
}
</script>

<script type="application/javascript" src="http://www.anotherdomain.com/file.php?callback=getip"> </script>

Simple as that!

Side note: Be sure to clean your $_GET if you're using this in any public-facing environment!

Answer 6

I am aware this is an old question but my solution may assist others.

I find that the JSON(P) services which make this easy do not last forever but the following JavaScript works well for me at the time of writing.

<script type="text/javascript">function z (x){ document.getElementById('y').innerHTML=x.query }</script>
<script type='text/javascript' src='http://ip-api.com/json/zero.eu.org?callback=z'></script>

The above writes my server's IP on the page it is located but the script can be modified to find any IP by changing 'zero.eu.org' to another domain name. This can be seen in action on my page at: http://meon.zero.eu.org/

Answer 7

There's a third-party service which provides a CORS-friendly REST API to perform DNS lookups from the browser - https://exana.io/tools/dns/

Answer 8

As many people said you need to use an external service and call it. And that will only get you the DNS resolution from the server perspective.

If that's good enough and if you just need DNS resolution you can use the following Docker container:

https://github.com/kuralabs/docker-webaiodns

Endpoints:

[GET] /ipv6/[domain]: Perform a DNS resolution for given domain and return the associated IPv6 addresses.

 {
     "addresses": [
         "2a01:91ff::f03c:7e01:51bd:fe1f"
     ]
 }

[GET] /ipv4/[domain]: Perform a DNS resolution for given domain and return the associated IPv4 addresses.

 {
     "addresses": [
         "139.180.232.162"
     ]
 }

My recommendation is that you setup your web server to reverse proxy to the container on a particular endpoint in your server serving your Javascript and call it using your standard Javascript Ajax functions.

Answer 9

There is a javascript library DNS-JS.com that does just this.

DNS.Query("dns-js.com",
    DNS.QueryType.A,
    function(data) {
        console.log(data);
});

Answer 10

Doing this would require to break the browser sandbox. Try to let your server do the lookup and request that from the client side via XmlHttp.

Answer 11

I don't think this is allowed by most browsers for security reasons, in a pure JavaScript context as the question asks.

Answer 12

Firefox has a built-in API for this since v60, for WebExtensions:

https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/dns/resolve

Answer 13

sure you can do that without using any addition, just pure javascript, by using this method of dns browser.dns.resolve("example.com"); but it is compatible just with FIREFOX 60 you can see more information on MDN https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/dns/resolve

Answer 14

Maybe I missed the point but in reply to NAVY guy here is how the browser can tell you the 'requestor's' IP address (albeit maybe only their service provider).

Place a script tag in the page to be rendered by the client that calls (has src pointing to) another server that is not loaded balanced (I realize that this means you need access to a 2nd server but hosting is cheap these days and you can set this up easily and cheaply).

This is the kind of code that needs to be added to client page:

On the other server "someServerIown" you need to have the ASP, ASPX or PHP page that;

----- contains server code like this:

"<% Response.Write("var clientipaddress = '" & Request.ServerVariables("REMOTE_ADDR") & "';") %>" (without the outside dbl quotes :-))

---- and writes this code back to script tag:

   var clientipaddress = '178.32.21.45';

This effectively creates a Javascript variable that you can access with Javascript on the page no less.

Hopefully, you access this var and write the value to a form control ready for sending back.

When the user posts or gets on the next request your Javascript and/or form sends the value of the variable that the "otherServerIown" has filled in for you, back to the server you would like it on.

This is how I get around the dumb load balancer we have that masks the client IP address and makes it appear as that of the Load balancer .... dumb ... dumb dumb dumb!

I haven't given the exact solution because everyone's situation is a little different. The concept is sound, however. Also, note if you are doing this on an HTTPS page your "otherServerIOwn" must also deliver in that secure form otherwise Client is alerted to mixed content. And if you do have https then make sure ALL your certs are valid otherwise client also gets a warning.

Hope it helps someone! Sorry, it took a year to answer/contribute. :-)

Answer 15

My version is like this:

php on my server:

<?php
    header('content-type: application/json; charset=utf-8');

    $data = json_encode($_SERVER['REMOTE_ADDR']);


    $callback = filter_input(INPUT_GET, 
                 'callback',
                 FILTER_SANITIZE_STRING, 
                 FILTER_FLAG_ENCODE_HIGH|FILTER_FLAG_ENCODE_LOW);
    echo $callback . '(' . $data . ');';
?>

jQuery on the page:

var self = this;
$.ajax({
    url: this.url + "getip.php",
    data: null,
    type: 'GET',
    crossDomain: true,
    dataType: 'jsonp'

}).done( function( json ) {

    self.ip = json;

});

It works cross domain. It could use a status check. Working on that.

Answer 16

If the client has Java installed, you could do something like this:

ipAddress = java.net.InetAddress.getLocalHost().getHostAddress();

Other than that, you will probably have to use a server side script.