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Nullish Coalescing (??)

Easy

In plain terms

?? returns the right-hand side when the left is null or undefined. Unlike ||, it does not treat 0, "", or false as "empty" - only null and undefined trigger the fallback.

What you need to know

  • •Returns right when left is null or undefined
  • •Does not treat 0, "", false as empty
  • •ES2020 feature

Try it yourself

Copy the code below and run it in your browser console or a code editor:

null ?? 'default';    // "default"
undefined ?? 'default'; // "default"

0 ?? 100;   // 0 (0 is not nullish)
'' ?? 'default';  // "" (empty string is not nullish)
false ?? true;    // false

// || treats 0, '', false as falsy
0 || 100;   // 100
0 ?? 100;   // 0

// Chaining
const value = a ?? b ?? c ?? 'final';

Learn more

Dive deeper with these trusted resources:

MDNjavascript.infoTutorialsPointW3Schools