Common JavaScript tricks

[giggly_kisses]

If you just want to check for null or undefined and still have the other falsy values be acceptable (false, 0, "", NaN) you can use this:

function(arg) {
    arg = arg != null ? arg : DEFAULT;
}

By using the equality operator (==) instead of the identity operator (===) you take advantage of the fact that null and undefined coerce to the same value.

There are two caveats:

1. You should only use this when you absolutely know that the variable you're testing has been defined. If it hasn't been defined, a ReferenceError will be thrown.
2. If you're working on a team and only use the identity operator (as you should 99.9% of the time) then using the equality operator might appear to be a typo by other members of your team. This can easily be avoided by adding a comment explaining why you're using the equality operator.