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Core JavaScriptBeginner

Nullish Coalescing

Nullish coalescing provides a fallback only when a value is `null` or `undefined`.

The `??` operator is similar to `||`, but it is more precise. It only falls back when the left side is actually missing, not when it is `0`, `false`, or an empty string. This makes it safer for default values when valid data can be falsy.

Explanation

The `??` operator is similar to `||`, but it is more precise. It only falls back when the left side is actually missing, not when it is `0`, `false`, or an empty string. This makes it safer for default values when valid data can be falsy.

Key Points

  • `??` only falls back for `null` or `undefined`.
  • It is often better than `||` when `0`, `false`, or `""` are valid inputs.
  • It pairs naturally with optional chaining.

Common Mistakes

  • Using `||` and accidentally replacing valid falsy values.
  • Expecting `??` to treat every falsy value as missing.
  • Mixing `??` and `||` carelessly without understanding precedence.

Practice Workspace

nullish-coalescing.js

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nullish-coalescing.js
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Related Concepts

Type Coercion

Type coercion is JavaScript converting one value type into another during operations or comparisons.

Truthy and Falsy

JavaScript treats some values as truthy and some as falsy when evaluating conditions.

Optional Chaining

Optional chaining safely reads nested properties without throwing when an intermediate value is missing.

Practice Challenges

Keep valid falsy values

7 min

Use nullish coalescing so valid values like `0` are not replaced by defaults.