Identifying a plain object in pure JS

I'm trying to write a node.js script and want to keep the dependencies on the minimum. I want to make sure that a given argument called config is a plain object, like this:

var config = {
  'key1': 'val1',
  'key2': 'val2',
  'key3': 'val3'
  /* ... */
}

Now the first thing that came to mind was something like this:

if (Object.prototype.toString.call(config) !== '[object Object]') {
  /* ... */
}

Can anyone think of an example where this wouldn't hold? I thought it was better to add:

if (typeof config !== 'object' ||
  Object.prototype.toString.call(config) !== '[object Object]') {
  /* ... */
}

just to be sure! But I'm still not convinced it could be this easy. I need

• Critical analysis: is it unsafe, is it an overkill or is it plain wrong! Any reason not to use this.
• A better way: something that you would do instead.

Thank you very much for your time folks.

I had a look at jQuery source, and particularly at the function jQuery.isPlainObject() and it uses a slightly more complex approach. Where I am looking to establish if it's a plain object, jQuery is making sure it's not anything other than a plain object. Have a look here:

isPlainObject: function( obj ) {
    // Not plain objects:
    // - Any object or value whose internal [[Class]] property is not "[object Object]"
    // - DOM nodes
    // - window
    if ( jQuery.type( obj ) !== "object" || obj.nodeType || jQuery.isWindow( obj ) ) {
        return false;
    }

    if ( obj.constructor &&
            !hasOwn.call( obj.constructor.prototype, "isPrototypeOf" ) ) {
        return false;
    }

    // If the function hasn't returned already, we're confident that
    // |obj| is a plain object, created by {} or constructed with new Object
    return true;
}