Two functions to traverse a chain of objects in Javascript. One to ask for a value at the end and one to place a value and create the intermediate objects if necessary. Both accept a variable length parameter's list or an array.

object_traverse.js

/**
 * Tries to follow a chain of objects starting at base and return the value at
 * the end. It uses a string array "mixedChain" to represent the chain and also
 * accepts a variable number of string parameters representing the same chain so
 * ask(object, ["child1", "child2"]) is equivalent to
 * ask(object, "child1", "child2")
 * If the chain keys are not strings convert them or use the array syntax
 *
 * @param {Object} base Root object of the chain to be inspected.
 * @param {array[String] | ...String} mixedChain List of strings representing
 *     the objects properties chain.
 * @return {mixed} value of the property at the end of the chain or undefined
 *     if not found.
 */
var ask = function(base, mixedChain) {
	var i = 0;
	var chain = mixedChain;
	if (Object.prototype.toString.call(chain) !== '[object Array]') {
		chain = arguments;
		i = 1;
	}
	while (i < chain.length - 1 && base !== undefined) {
		base = base[chain[i]] || undefined;
		i++;
	}
	return base ? base[chain[i]] : undefined;
};

/**
 * Builds a chain of objects if they don't exist and places a value at the end.
 * It uses a string array "mixedChain" to represent the chain and also
 * accepts a variable number of string parameters representing the same chain, or a
 * single dot separated string that will be splitted and used as chain
 * If the chain keys are not strings convert them or use the array syntax
 * The last parameter is always the value to be placed.
 * build(object, ["child1", "child2"], value) is equivalent to
 * build(object, "child1", "child2", value) and equivalent to
 * build(object, "child1.child2", value)
 *
 * @param {Object} base Root object of the chain to be used.
 * @param {array[String] | ...String | String} mixedChain List of strings representing
 *     the objects properties chain. If it is a dot separated string, the string is splitted
 *     and used as if it were an array. (Use the array version if your second property names may have dots)
 * @param {mixed} mixedVal Value to be placed at the end of the chain, it
 *     represents the last parameter although, positionally, it's the third. If it is an objects
 *     it will merge it's contents
 */
var build = function(base, mixedChain, mixedVal) {
	var args_index = 0;
	var chain = mixedChain;
	var val = mixedVal;
	var isArray = Object.prototype.toString.call(chain) === '[object Array]';
	if (!isArray) {
		var splitted = chain.split('.');
		if (splitted.length < 2) {
			chain = arguments;
			//if the chain is the arguments object avoid the base argument
			args_index = 1;
		} else {
			chain = splitted;
		}
		val = arguments[arguments.length - 1];
	}
	var i = args_index;
	while (i < chain.length - args_index - 1) {
		if (base[chain[i]] === undefined) {
			base[chain[i]] = {};
		}
		base = base[chain[i]];
		i++;
	}
	if (typeof val === 'object') {
		base[chain[i]] = Object.assign(base[chain[i]] || {}, val);
	} else {
		base[chain[i]] = val;
	}
};