Predicates & Type Guards

Runtime Validation with Precision

NHB Toolbox provides two complementary validation tools:

1. Predicate Functions (Boolean Validators)

Simple functions that return boolean without affecting TypeScript's type system:

const prime = isPrime(number); // Returns true/false

2. Type Guards (Type Narrowing)

Functions using x is T syntax that narrow types in conditional blocks:

if (isString(input)) { // input is now narrowed to string type
  input.toLowerCase(); // Type-safe access
}

Key Differences

Feature	Predicates	Type Guards
Return type	boolean	value is Type
Type narrowing	No	Yes
Usage	Anywhere	Conditionals
Example	isPrime(value)	isString(value)

Why This Matters

• Predicates for simple validation
• Guards when you need type narrowing

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