set.js

 
function set(obj, keys, value){
 
    // for empty or undefined paths, just assume root
    if (!keys) {
        return obj;
    }
 
    var parts = keys.split("."), o = obj;
 
    for (var i=0; i < parts.length - 1; i++) {
        var part = parts[i];
 
        if (typeof o !== "object") {
            return false;
        }
 
        o = o[part];
    }
 
    if (typeof o === "undefined") {
        return false;
    }
 
    o[parts[parts.length - 1]] = value;
}
 
// for example:
var o = {
  b: ["a", "b", "c"],
  d: {
    e: {
      q: 1
    }
  }
}
 
set(o, "b.2") // => "c"
set(o, "d.e.q") // => 1