externalLinks function causes links to outside resources to open in a new window.

externalLinks.js

/**
 * @fileoverview externalLinks function, which sorts
 * through all of the links on a given page, and if they are
 * http:, https:, or mailto: links, a class is applied and their
 * target is set to _blank. Also includes supporting addClass
 * function, which appends CSS classes to elements without
 * over-writing existing classes.
 * @author Andrew Noyes [email protected]
 */

/**
 * Adds a class to an element without
 * over-writing previously existing classes.
 * @param elem {HTMLElement} HTML element to add class to
 * @param newClass {String} Class to add to HTML element
 */
function addClass(elem, newClass) {
	if (!!elem.className.length) {	// If className has a length
		newClass = " " + newClass;
	}
	elem.className += newClass;
}

/**
 * Finds all anchor elements with an href
 * attribute that begins with a protocol and sets
 * its target attribute to "_blank", causing
 * their target URL to open in a new window. It
 * then applies the protocol name as a CSS class.
 */
function externalLinks() {
	// Object detection
	if (!document.getElementsByTagName) {
		return false;
	}
	
	// Variable declarations
	var links, i, il, href, protocol;
	
	links = document.getElementsByTagName("a");
	for (i = 0, il = links.length; i < il; i++) {
		href = links[i].getAttribute("href", 2);	// Second argument ensures IE returns attribute text
		protocol = href.substr(0, href.indexOf(":"));
		if (!!protocol.length) {
			links[i].target = "_blank";
			addClass(links[i], protocol);
		}
	}
}