Recursively extract keys from nested object

gistfile1.js

var object = {
  hello: 'world',
  hallo: {
    german: 'welt',
    test: {
      test: true,
      test: false
    }
  }
};

var keys = function (object) {
  var keys = {};
  
  var recurse = function (object) {
    if (typeof object !== 'object') return;
    
    for (var key in object) {
      keys[key] = true;
      recurse(object[key]);
    }
  };
  
  recurse(object);
  
  return Object.keys(keys);
};

console.log(keys(object));