For those "external links should open in new tabs" clients…

external.vanilla-forEach.js

// Array.forEach potentially faster than loop
// http://jsperf.com/testing-foreach-vs-for-loop
var links = document.querySelectorAll('a[href*="//' + window.location.host +'"]');

[].slice.call(links).forEach(function(a) {
  a.target = '_blank';
});

external.vanilla-loop.js

var a = document.querySelectorAll('a[href*="//' + window.location.host +'"]'),
    length = a.length;

for(var i = 0; i < length; ++i) {
  a[i].target = '_blank';
}