Get deeply nested object properties, ES5 compatible - good replacement for LoDash' .get()

getDeep.js

/**
 * getDeep(object, pathString, defaultValue)
 *
 * Tries to find the pathString inside the object. Returns defaultValue if any 
 * check along the way returns undefined. 
 * 
 * ES5 compatible, for when you need to support things like IOT toasters running IE6 
 * or shamefully out-of-date SAP/Citrix combinations.
 * 
 * Replaces lengthy checks like this:
 * 
 * var foo = (typeof obj != 'undefined' 
 *		&& obj.length > 0
 * 		&& typeof obj[1].prop1 !== 'undefined' 
 * 		&& typeof obj[1].prop1.prop2 !== 'undefined'
 *		&& typeof obj[1].prop1.prop2["prop.3"] !== 'undefined')
 *	? obj.prop1.prop2["prop.3"] 
 *	: null;
 *
 * with checks like this:
 * var foo = getDeep(obj, 'obj[1].prop1.prop2["prop.3"]', null);
 *
 */
var getArrayIndexFromString = function (str) {
	var containsArray = /\[(\d+)\]/g;
	var idx = containsArray.exec(str);
	return (idx !== null) ? idx[1] : null;
};

var walkThroughObj = function(total, currentValue) {
	if (typeof total == 'undefined' || total === null) { return null; }
	
	var idx = getArrayIndexFromString(currentValue);
	var objArrName = currentValue.slice(0, currentValue.indexOf('['));
	var format = idx ? total[objArrName][parseInt(idx)] : total[currentValue];
	return (typeof format !== "undefined") ? format : null;
};

var getDeep = function (obj, path, defaultValue) {
  var result = String.prototype.split.call(path, /(\w+\[\d\])|(\W)/)
	.filter(Boolean)
	.filter(function(e) { return e.match(/^\w+/g); })
	.reduce(walkThroughObj, obj);
  return (typeof result == "undefined" || result === null || result === obj) ? defaultValue : result;
};