How do I add target="_blank" to a link within a specified div?

Let's say I have the following code:

<div id="link_other">
    <ul>
        <li><a href="http://www.google.com/">google</a></li>
        <li>
            <div class="some_class">
                dsalkfnm sladkfm
                <a href="http://www.yahoo.com/">yahoo</a>
            </div>
        </li>
    </ul>
</div>

In this case, the JavaScript would add target="_blank" to all links within the div link_other.

How can I do that using JavaScript?

/* here are two different ways to do this */
//using jquery:
$(document).ready(function(){
  $('#link_other a').attr('target', '_blank');
});

// not using jquery
window.onload = function(){
  var anchors = document.getElementById('link_other').getElementsByTagName('a');
  for (var i=0; i<anchors.length; i++){
    anchors[i].setAttribute('target', '_blank');
  }
}
// jquery is prettier. :-)

You could also add a title tag to notify the user that you are doing this, to warn them, because as has been pointed out, it's not what users expect:

$('#link_other a').attr('target', '_blank').attr('title','This link will open in a new window.');

Non-jquery:

// Very old browsers
// var linkList = document.getElementById('link_other').getElementsByTagName('a');

// New browsers (IE8+)
var linkList = document.querySelectorAll('#link_other a');

for(var i in linkList){
 linkList[i].setAttribute('target', '_blank');
}

Bear in mind that doing this is considered bad practice in general by web developers and usability experts. Jakob Nielson has this to say about removing control of the users browsing experience:

> Avoid spawning multiple browser windows if at all possible — taking the "Back" button away from users can make their experience so painful that it usually far outweighs whatever benefit you're trying to provide. One common theory in favor of spawning the second window is that it keeps users from leaving your site, but ironically it may have just the opposite effect by preventing them from returning when they want to.

I believe this is the rationale for the target attribute being removed by the W3C from the XHTML 1.1 spec.

If you're dead set on taking this approach, Pim Jager's solution is good.

A nicer, more user friendly idea, would be to append a graphic to all of your external links, indicating to the user that following the link will take them externally.

You could do this with jquery:

$('a[href^="http://"]').each(function() {
    $('<img width="10px" height="10px" src="/images/skin/external.png" alt="External Link" />').appendTo(this)

});

Using jQuery:

 $('#link_other a').each(function(){
  $(this).attr('target', '_BLANK');
 });

I use this for every external link:

window.onload = function(){
  var anchors = document.getElementsByTagName('a');
  for (var i=0; i<anchors.length; i++){
  	if (anchors[i].hostname != window.location.hostname) {
  		anchors[i].setAttribute('target', '_blank');
  	}
  }
}

Inline:

$('#link_other').find('a').attr('target','_blank');

Use this for every external link

$('a[href^="http://"], a[href^="https://"]').attr('target', '_blank');