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This short post introduces a useful JavaScript operator to help make your one-liners even more concise.
The specification [1] was added formally in the 11th edition of ECMAScript. It is implemented as a logical operator to selectively return the result of one of two expressions (or operands) based on one of the expressions resolving to a "nullish" value. A nullish value in JavaScript is one that is `null` or `undefined`.
In particular, the operator - given by `??` - will return the right-hand side if the left-hand expression resolves to `null` or `undefined`, and otherwise returns the left-hand side.
const x = y ?? z;
In the example above, `z` will be returned if `y` is "nullish", and otherwise `y` will be returned.
Nullish coalescing is similar to (but stricter than) the more commonly-seen logical OR operator - given by `||` - which returns the result of the right-hand side expression if the left-hand side resolves to any falsy value, which includes nullish ones in addition to the boolean `false`, empty string (`''`), `0`, `NaN`, etc.
More info is available on MDN [2] and Wikipedia discusses null coalescing in other languages [3].