isValid

isValid is a common predicate name used in programming to indicate whether a value, object, or state satisfies a defined set of rules. Typically, an isValid function or property returns a boolean: true if the input passes validation and false otherwise. The term isValid is language-agnostic and appears across many domains, from data validation to state management.

In practice, isValid covers a wide range of checks. It can assess simple formats such as email addresses or dates, verify that numeric values fall within allowed ranges, or confirm that complex data structures conform to a schema. It is also used to indicate the validity of tokens, messages, or resources, for example whether a security token is still valid or whether a user-provided object satisfies invariant constraints.

Design and implementation considerations include clarity, testability, and maintainability. Validators are often composed of smaller, reusable predicates to promote readability and reuse. It is common to separate validation rules from business logic, provide meaningful error information alongside validity results, and ensure deterministic behavior through pure functions where possible. It is also important to validate on the server side in addition to client-side checks to guard against tampering or bypassing client validations.

A note on scope: what counts as valid is domain-specific and may change as requirements evolve. Therefore, isValid implementations should be well-documented, versioned, and aligned with the applicable validation strategy, whether it be format checking, schema validation, or business-rule enforcement. See also: data validation, input validation, and schema validation.