Deep copy (recursively) properties from one object into another

extend.js

/*
 * Extend an object
 *
 * Deep copies (recursively) properties from source into target
 */
function extend (target, source) {
    var prop;
    for (prop in source) {
        if (Object.prototype.hasOwnProperty.call(source, prop)) {
            if (typeof source[prop] === 'object') {
                if (source[prop] instanceof Array) {
                    target[prop] = source[prop].slice(0);
                } else {
                    target[prop] = {};
                    extend(target[prop], source[prop]);
                }
            } else {
                target[prop] = source[prop];
            }           
        }
    }
}