How best to determine if an argument is not sent to the JavaScript function

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I have now seen 2 methods for determining if an argument has been passed to a JavaScript function. I’m wondering if one method is better than the other or if one is just bad to use?

 function Test(argument1, argument2) {
      if (Test.arguments.length == 1) argument2 = 'blah';

      alert(argument2);
 }

 Test('test');

Or

 function Test(argument1, argument2) {
      argument2 = argument2 || 'blah';

      alert(argument2);
 }

 Test('test');

As far as I can tell, they both result in the same thing, but I’ve only used the first one before in production.

Another Option as mentioned by Tom:

function Test(argument1, argument2) {
    if(argument2 === null) {
        argument2 = 'blah';
    }

    alert(argument2);
}

As per Juan’s comment, it would be better to change Tom’s suggestion to:

function Test(argument1, argument2) {
    if(argument2 === undefined) {
        argument2 = 'blah';
    }

    alert(argument2);
}

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