What is the best way to turn strings into an JSON object with nested keys in Node.js?

I have the following input:

  var input = {
    "usa.ca.los": 12345,
    "usa.ca.sfo": 12346,
    "usa.ws.sea": 22333, 
    "others.a.b.c.d.e": 33333
  }

and I want to turn it into:

 var output = {
     "usa": {
             "ca": {
                     "los": 12345,
                     "sfo": 12346,
                   },
             "ws": {
                     "sea": 22333
                   }
            }
     "others":{"a":{"b":{"c":{"d":{"e":33333}}}}}
 }

I know I can use a recursive function and construct the output but seems like too much work.

Since my program in in Node.js, is there a simpler way to do it using underscore.js? or some other existing functions can make me do the conversion properly?

I don't think theres an inbuilt function in underscore to do that, but its a fairly simple matter to write one yourself:

var input = {
    "usa.ca.los": 12345,
    "usa.ca.sfo": 12346,
    "usa.ws.sea": 22333, 
    "others.a.b.c.d.e": 33333
}

function parse(input){
    var output = {};
    for(var key in input){
        setByString(output, input[key], key);
    }

    return output;
}

function setByString(obj, value, key){
    var split = key.split('.');
    while(split.length){
        key = split.shift();
        if(split.length){
            if(!obj.hasOwnProperty(key)){
                obj[key] = {};
            }
            obj = obj[key];
        } else {
            obj[key] = value;
        }
    }
}

console.log(parse(input));