Nullish coalescing

⬅️ FEM TypeScript Fundamentals

Nullish coalescing ??

• null means there’s a value, and the value is nothing
• undefined means the value isn’t available (yet)
• similar to the JavaScript logical OR operator, ||. But unlike ||, it doesn’t treat 0 and '' as falsey.
• aka “returning the first value that isn’t null or undefined”

1 ?? 'default' === 1
0 ?? 'default' === 0
'a' ?? 'default' === 'a'
'' ?? 'default' === ''
null ?? 'default' === 'default'
undefined ?? 'default' === 'default'

function numberOrOne(n: number | undefined): number {
  return n ?? 1;
}
[numberOrOne(3), numberOrOne(undefined), numberOrOne(0)];
 
// Result:
[3, 1, 0]