Look who managed to head to my blog only to find himself reading an article about a tweeted Javascript quiz. In this series, I try to break such down, and this post features a lesser-known but often useful operator: Nullish Coalescing!

The Snippet

console.log(1 === null ?? 1)

This time we have a super quick one. It logs a logical expression to the console. And that's pretty much already it! The expression itself consists of two parts. The first one compares null to 1. The result is the left-hand side operand of a so-called “Nullish Coalescing Operator” typed as ??. The right-hand side operand is, again, just 1.

The Output

The output is also pretty straightforward. At least if you know what a “nullish coalescing operator” does. This expression will log false to the console.

The Analysis

For the analysis, we start with the Strict Equal Operator (===) as it takes higher precedence (“will be evaluated before”) than the mysterious two question marks. And it's also reasonably easy. Comparing null to 1 will undoubtedly result in false, won't it? What's left looks something like: false ?? 1. So far, so good. Now comes the fun part. A Nullish Coalescing Operator works in its core like a Logical Or (||). However, instead of checking for falsy values, it only validates for nullish ones! That means either null or undefined. To get this straight: it will return the left-hand side value if it's not “nullish” or the right-hand side value if not. And that is the reason false gets printed to the console. 🥧

Further Reading

– Nullish Coalescing Operator – Operator Precedence