LogoJuan Manuel Allo Ron

Tip: Watch out for null in default params

By Juan Manuel Allo Ron on Jun 4, 2020
A pattern formed with the null word

Defaults in function parameters is a feature that simplified my code a lot. But there is one caveat that we need to be aware of! Let’s start with an example:

function say(message = 'Hello World') {

Now, what’s the output of the following statements:


Most of them will work as you would expect…but there is always a trick in JS… when calling say(null) as null is a value, the default won’t be triggered causing null to be logged. In this example is easy to see it quickly, but this gets trickier in real world applications.

How do we avoid this?

I try not to use null at all and that tends to reduce this problem. Are you using any other solution? I would love to hear about it.


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