isNegativeInteger

Checks whether a value is a negative integer.

This helper never throws and never mutates input. Returns true only if the value is a finite number primitive, has no fractional component, and is strictly less than zero.

Strings, objects, arrays, booleans, boxed numbers, fractional values, and non‑finite numbers are rejected.

Signature

function isNegativeInteger(value: unknown): value is number

Parameters

Name	Type	Description
value	unknown	The value to check. Must be a finite number less than zero (0).

Returns

true: If the value is a negative integer. false: Otherwise.

Examples

isNegativeInteger(-1);        // → true
isNegativeInteger(-42);       // → true

isNegativeInteger(-1.5);      // → false
isNegativeInteger(0);         // → false
isNegativeInteger(7);         // → false
isNegativeInteger("5");       // → false
isNegativeInteger(NaN);       // → false
isNegativeInteger(-Infinity); // → false

Notes

• Zero is not considered negative.
• Fractional values are rejected; the value must be an integer.
• Only number primitives are accepted; boxed numbers (new Number(-3)) are rejected.
• Never throws. Always returns a boolean.
• Use validateNegativeInteger if you need a structured ValidationResult with error details.