mout/object/deepFillIn.js

var forOwn = require('./forOwn');
var isPlainObject = require('../lang/isPlainObject');

    /**
     * Deeply copy missing properties in the target from the defaults.
     */
    function deepFillIn(target, defaults){
        var i = 0,
            n = arguments.length,
            obj;

        while(++i < n) {
            obj = arguments[i];
            if (obj) {
                // jshint loopfunc: true
                forOwn(obj, function(newValue, key) {
                    var curValue = target[key];
                    if (curValue == null) {
                        target[key] = newValue;
                    } else if (isPlainObject(curValue) &&
                               isPlainObject(newValue)) {
                        deepFillIn(curValue, newValue);
                    }
                });
            }
        }

        return target;
    }

    module.exports = deepFillIn;