deepMerge function for underscore.js

deepmerge.js

deepMerge: function(dest){
  _.each(_.rest(arguments), function(source){
    var sourceVal, destVal;
    for (var prop in source){
      sourceVal = source[prop];
      destVal = dest[prop];
      if (prop in dest && _.isObject(sourceVal) && _.isObject(destVal)){
        _.deepMerge(destVal, sourceVal);
      } else {
        dest[prop] = sourceVal;
      }
    }
  });
  return dest;
}

deepmerge_tests.js

module("_.deepMerge");

test("flat objects", function(){
  var obj = {foo: 'bar'};
  _.deepMerge(obj, {baz: 'blip'});
  deepEqual(obj, {
    foo: 'bar',
    baz: 'blip'
  });
});

test("nested objects", function(){
  var obj = {
    foo: {
      bar: 'baz'
    }
  };

  _.deepMerge(obj, {
    foo: {
      hi: 'there'
    }
  });

  deepEqual(obj, {
    foo: {
      bar: 'baz',
      hi: 'there'
    }
  });
});