JavaScript function to extend an object

extend.js

/**
 * Extends obj by adding the properties of all other objects passed to the function.
 *
 * @param {...Object} obj
 * @returns {Object} The extended object.
 */
function extend(obj) {
    for (var i = 1; i < arguments.length; i++) {
        for (var key in arguments[i]) {
            if (arguments[i].hasOwnProperty(key)) {
                obj[key] = arguments[i][key];
            }
        }
    }

    return obj;
}