Journey of Nullish coalescing operator (?? 😮)

Abhishek Saxena
2 min readJun 24, 2020

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Hey folks!!!

Today we are going into one new topic of javascript or i can say modern javascript 🤨.

Nullish coalescing operator…wait!! even i am not able to pronounce it 😶, but who cares 😋.

Let’s start the journey !!!!!!😎

The nullish coalescing operator ?? provides a short syntax for selecting a first “defined” variable from the list.

The result of a ?? b is:

  • a if it’s not null or undefined,
  • b, otherwise.

So, x = a ?? b is a short equivalent to:

x = (a !== null && a !== undefined) ? a : b;

Yeahhh!!!!! we decoded the mystery 😎….

But why to use this, we already have different methods for this.🤐

So, this came into picture when we have some issues (not exactly the issues.. i guess🙄 ) with OR (||) operator.

Comparison with OR (||)

The OR || operator can be used in the same way as ??. Actually, we can replace ?? with || in the code above and get the same result.

The important difference is that:

  • || returns the first truthy value.
  • ?? returns the first defined value.

This matters a lot when we’d like to treat null/undefined differently from 0😯.

Lot of theory now. Let’s look a example 😇

money = money ?? 100;

This sets money to 100 if it’s not defined.

Let’s compare it with ||:

Here, money || 100 treats zero money as unset, same as null, undefined or any other falsy value. So the result is 100.

The money ?? 100 returns 100 only if money is exactly null or undefined. So the alert shows the money value 0 “as is”.

Which behavior is better depends on a particular use case. When zero money is a valid value😥 , then ?? is preferable.

Waitt.. It will not work in IE😥.But no issues ‘Polyfills are the saviours😇’

Thank you for reading 🙌

Clap! if this was useful for you 👋

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Abhishek Saxena

Working as a full time Front-End developer & also searching web for some cool stuff.