javascript - Recursive/deep extend/assign in Underscore.js?

Question

Is there any way to get Underscore.js extend function:

Copy all of the properties in the source objects over to the destination object, and return the destination object. It's in-order, so the last source will override properties of the same name in previous arguments.

... to work recursively?

Actually, query property in creditOperation is going to completely override the query property defined in baseOperation:

var url = require('url')
  , _ = require('underscore'),
  , baseOperation = {
        host: 'gateway.skebby.it',
        pathname: 'api/send/smseasy/advanced/http.php',
        protocol: 'https',
        query: {
            'username': 'foo',
            'password': 'bar',
        }
    };

var creditOperation = _.extend(baseOperation, {
    query: {
        'method': 'baz'
    }
});

console.log(url.format(creditOperation));

I'd like to obtain this creditOperation:

{
    host: 'gateway.skebby.it',
    pathname: 'api/send/smseasy/advanced/http.php',
    protocol: 'https',
    query: {
        'username': 'foo',
        'password': 'bar',
        'method': 'baz'
    }
}

Answer 1

With Lodash (fork of underscore) you can. Lodash's _.extend method accept third (or higher) parameter to be a function, that receives values (old and new); So you can do something like this:

var deep = function(a, b) {
    return _.isObject(a) && _.isObject(b) ? _.extend(a, b, deep) : b;
};

var a = {a:{b:{c:1}}},
    b = {a:{b:{z:1}}};

_.extend(a,b,deep);

upd. As Paolo Moretti said in comments, there is the same function in lodash called _.merge:

_.merge(a,b);