function isNumber(arg) {
  return typeof arg === 'number' || arg instanceof Number;
}
Merge object b with object a.

    var a = { foo: 'bar' }
      , b = { bar: 'baz' };

    utils.merge(a, b);
    // => { foo: 'bar', bar: 'baz' }

@param {Object} a
@param {Object} b
@return {Object}
@api private