Nullish coalescing operator
A conditional operator that yields its left operand unless it is null or an equivalent absent value, in which case it yields a fallback right operand.
Pro Angular 16
The nullish coalescing operator returns its right operand only when its left operand is null or undefined.
- How it is used
- Supplies defaults for null or undefined values while preserving zero in TypeScript expressions and Angular class bindings.
- How deep it goes
- Defines the operator through console examples and works through a comparison-precedence pitfall, without examining runtime internals.
- Examples
- Uses browser-console results for undefined, a string, and zero, then applies a missing-price fallback to CSS class selection.
- What you can do after
- Practice/perform it by replacing truthiness-based fallbacks with `??` and parenthesizing coalesced values before comparisons.
Read how Pro Angular 16 explains nullish coalescing operator →
Essential TypeScript 5, Third Edition
The nullish coalescing operator returns its right-hand operand only when its left-hand operand is null or undefined.
- How it is used
- Supplies defaults for missing rates and object properties while preserving valid falsy values.
- How deep it goes
- Explains operand behavior through worked JavaScript expressions and applies it to property access without examining operator internals.
- Examples
- Uses a zero-rated tax calculation, object-price fallbacks, and a missing indexed product.
- What you can do after
- Diagnose/debug with it when logical OR replaces a legitimate zero or an optional property needs a fallback.
Read how Essential TypeScript 5, Third Edition explains nullish coalescing operator →
Kotlin in Action, 2E
The Elvis operator `?:` evaluates its left operand when non-null and otherwise evaluates and returns its right operand.
- How it is used
- Provides defaults or immediate control-flow exits when nullable expressions lack usable values.
- How deep it goes
- Explains evaluation, safe-call combinations, defaults, and throw-based validation through compact Kotlin examples.
- Examples
- Uses nullable string lengths, names, nested company addresses, shipping labels, and missing person ages.
- What you can do after
- Apply it to replace null with defaults or enforce preconditions using return and throw expressions.
Read how Kotlin in Action, 2E explains nullish coalescing operator →
Related concepts
- logical ORcontrasts with · Logical OR is a Boolean disjunction that evaluates to true when at least one operand or condition is true.
- missing valueuses · A missing value is a marker or condition indicating that an expected data value or reference is absent, unavailable, unknown, or inapplicable.
- null operatorkind of · The null-conditional operator conditionally accesses a member or element when its receiver is non-null and otherwise produces null.
- truthinesscontrasts with · Truthiness is a programming language’s rule for interpreting values as true or false in a Boolean context.
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