Test if links are external with jQuery / javascript?

I know this post is old but it still shows at the top of results so I wanted to offer another approach. I see all the regex checks on an anchor element, but why not just use window.location.host and check against the element's host property?

function link_is_external(link_element) {    return (link_element.host !== window.location.host);}

With jQuery:

$('a').each(function() {    if (link_is_external(this)) {        // External    }});

and with plain javascript:

var links = document.getElementsByTagName('a');for (var i = 0; i < links.length; i++) {    if (link_is_external(links[i])) {        // External    }}

var comp = new RegExp(location.host);$('a').each(function(){   if(comp.test($(this).attr('href'))){       // a link that contains the current host                  $(this).addClass('local');   }   else{       // a link that does not contain the current host       $(this).addClass('external');   }});

Note: this is just a quick & dirty example. It would match all href="#anchor" linksas external too. It might be improved by doing some extra RegExp checking.

Update 2016-11-17

This question still got a lot of traffic and I was told by a ton of people that this accepted solution will fail on several occasions. As I stated, this was a very quick and dirty answer to show the principal way how to solve this problem. A more sophisticated solution is to use the properties which are accessible on a <a> (anchor) element. Like @Daved already pointed out in this answer, the key is to compare the hostname with the current window.location.hostname. I would prefer to compare the hostname properties, because they never include the port which is included to the host property if it differs from 80.

So here we go:

$( 'a' ).each(function() {  if( location.hostname === this.hostname || !this.hostname.length ) {      $(this).addClass('local');  } else {      $(this).addClass('external');  }});

State of the art:

Array.from( document.querySelectorAll( 'a' ) ).forEach( a => {    a.classList.add( location.hostname === a.hostname || !a.hostname.length ? 'local' : 'external' );});

And the no-jQuery way

var nodes = document.getElementsByTagName("a"), i = nodes.length;var regExp = new RegExp("//" + location.host + "($|/)");while(i--){    var href = nodes[i].href;    var isLocal = (href.substring(0,4) === "http") ? regExp.test(href) : true;    alert(href + " is " + (isLocal ? "local" : "not local"));}

All hrefs not beginning with http (http://, https://) are automatically treated as local