The nullish coalescing operator is the newest addition to the JavaScript logical operator family. It was published in 2020.

There are three different logical operators in JavaScript: AND &&, OR ||, and then the nullish coalescing operator ??, which is kind of like the OR operator, but a bit smarter. For safe property access, the related optional chaining operator solves a different problem.

Recap of logical operators

The AND operator requires both sides of the condition to be the same for it to evaluate true:

console.log(true && true) // true
console.log(true && false) // false
console.log(false && false) // false
console.log(null && false) // null
console.log(null && true) // null
console.log(0 && false) // 0
console.log(0 && true) // 0
console.log('' && false) // ''
console.log('' && true) // ''
console.log(NaN && false) // NaN
console.log(NaN && true) // NaN

The OR operator works pretty much the opposite way, both of the sides have to be false for it to evaluate false:

console.log(true || true) // true
console.log(true || false) // true
console.log(false || false) // false
console.log(null || false) // false
console.log(null || true) // true
console.log(0 || false) // false
console.log(0 || true) // true
console.log('' || false) // false
console.log('' || true) // true
console.log(NaN || false) // false
console.log(NaN || true) // true

Nullish coalescing operator

The nullish coalescing operator (??) is a logical operator that returns its right-hand side operand when its left-hand side operand is null or undefined, and otherwise returns its left-hand side operand.

The nullish coalescing operator is kind of like OR, but it treats '', 0, and NaN as non-falsy, that’s essentially the only difference between OR and nullish coalescing.

console.log(true ?? true) // true
console.log(true ?? false) // true
console.log(false ?? false) // false
console.log(null ?? false) // false
console.log(null ?? true) // true
console.log(0 ?? false) // 0
console.log(0 ?? true) // 0
console.log('' ?? false) // ''
console.log('' ?? true) // ''
console.log(NaN ?? false) // NaN
console.log(NaN ?? true) // NaN

Conclusions

Now that most browsers are based on Chromium, the browser support for ?? is already pretty good. 92.14% globally at the moment of writing this.