Typeof operator
A typeof operator obtains type information about an operand or expression, yielding a type or a string describing its type depending on the language.
Modern C, Third Edition
typeof is a C type operator that derives a type from an expression or type name without evaluating an expression operand.
- How it is used
- Supplies expression-derived types for generic macros, type checks, result conversions, and an explicit enumeration underlying type.
- How deep it goes
- Works through declarations and macro type matching, including evaluation and qualifier cautions, rather than detailing every typeof edge case.
- Examples
- Uses a declaration inferred from `3*x`, a static-assertion compatibility macro, and an enumeration typed from a decimal constant.
- What you can do after
- Build it from scratch: use typeof with _Generic to check macro-argument types without evaluating the arguments.
Essential TypeScript 5, Third Edition
The typeof operator is a JavaScript operator that produces a string identifying the type category of a value.
- How it is used
- Identifies a value’s runtime type while demonstrating JavaScript’s dynamic typing.
- How deep it goes
- Demonstrates primitive results and the null exception, but stops short of broader object and function-type behavior.
- Examples
- Uses index.js and index.ts listings that inspect strings, numbers, booleans, undefined, and a changing variable.
- What you can do after
- Diagnose/debug with it by checking a value’s runtime category and spotting unexpected assignments before calculations fail.
Read how Essential TypeScript 5, Third Edition explains typeof operator →
Pro Angular 16
The typeof operator is a JavaScript operator that returns a string identifying the type of its operand.
- How it is used
- Uses runtime checks to validate function arguments and select operations for number, string, or object values.
- How deep it goes
- Demonstrates guards, errors, union-type branches, and object limitations, but defers a complete catalog of returned type strings.
- Examples
- Uses numeric and string function arguments, union-type branches, and Product and DiscountProduct objects.
- What you can do after
- Diagnose unexpected argument types and branch safely before applying type-specific operations.
Related concepts
- type inferenceused by · Type inference is the automatic deduction of program or expression types from available values, context, and constraints without requiring explicit type annotations.
- type guardused by · A type guard is a runtime-checkable condition that enables TypeScript to narrow an expression to a more specific type within a code path.
- tuplecontrasts with · A tuple is a finite, ordered collection of elements treated as a single composite value or record.
- type assertionalternative to · A type assertion is a language construct that states or checks that a value has a specified type, with runtime behavior depending on the language.
- objectcontrasts with · A computational object is a runtime entity or structured value representing data, state, or a resource, with properties or operations defined by its programming model.
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