distinguish falsy vs nullish

When handling potentially null or undefined values, carefully choose between the logical OR (||) and nullish coalescing (??) operators based on whether you want to preserve other falsy values.

The || operator treats all falsy values (null, undefined, false, 0, “”, NaN) as “missing” and provides the fallback. The ?? operator only treats null and undefined as “missing”, preserving other falsy values like empty strings or false booleans.

Use || when: You want to reject all falsy values and provide a default.

// Reject empty strings, use default
pathname: locationProp.pathname || "/"

Use ?? when: You want to preserve legitimate falsy values but handle null/undefined.

// Allow false, "", 0 but handle null/undefined
state: locationProp.state ?? null

Avoid || when falsy values are valid: Using || can cause bugs by rejecting legitimate values.

// BAD: Rejects "", false, 0, NaN as valid state values
state: locationProp.state || null

// GOOD: Only rejects null/undefined
state: locationProp.state ?? null

Consider bundle size implications when using ?? in environments with older transpilation targets, and use explicit null checks as an alternative: value != null ? value : fallback.