update an object given a slash-delimited path (where each element in path is a property) and a value

update.js

function update(path, val, obj) {
	(function r(keys, o) {
		if (keys.length > 1) {
			var current = keys.shift();
			if (!o[current])
				o[current] = isNaN(parseInt(keys[0])) ? {} : [];
			r(keys, o[current]);
		} else {
			o[keys[0]] = val;
		}
	})(path.split('/'), obj);
}