A simple extend function for JavaScript

extend.js

function extend(base) {
    var parts = Array.prototype.slice.call(arguments, 1);
    parts.forEach(function (p) {
        if (p && typeof (p) === 'object') {
            for (var k in p) {
                if (p.hasOwnProperty(k)) {
                    base[k] = p[k];
                }
            }
        }
    });
    return base;
}

Race condition prevention provided by single-threaded model of JS in browsers?
(in this use scenario: http://jsfiddle.net/katowulf/9GEFf/)