Access to object members by string path

objectByString.js

/**
 * @example Object.byString(someObject, 'part1.name')
 * @example Object.byString(someObject, 'part2.qty')
 * @example Object.byString(someObject, 'part3[0].name')
 *
 * @param obj {Object}
 * @param str {String}
 * @returns {*}
 */
Object.byString = function(obj, str) {
    if (str in obj) {
        return obj[str];
    }
    if (!(str.length) || (null === obj)) {
        return obj;
    }
    var a = str.replace(/\[(\w+)\]/g, '.$1').replace(/^\./, '').split('.'); // convert indexes to properties and strip a leading dot
    for (var i = 0, n = a.length; i < n; ++i) {
        var k = a[i];
        if ((null !== obj) && (k in obj)) {
            obj = obj[k];
        } else {
            return;
        }
    }
    return obj;
};