isBoolean
function isBoolean(value: unknown): value is boolean;
Only the two primitives pass. new Boolean(false) is an object, and the strings "true" and "false" are strings.
isX and nonX answer a question and never interrupt control flow; requireX and requireNonX hand the value back or throw. The scheme is explained in Validation conventions.
Parameters
Parameter | Type | Description |
|---|---|---|
|
| The value to check. |
Returns
boolean — true when the value is a boolean; otherwise false.
In TypeScript the guard narrows value to boolean inside the branch.
Examples
What passes and what does not
isBoolean(true); // => true
isBoolean(false); // => true
isBoolean("true"); // => false
isBoolean(1); // => false
isBoolean(null); // => false
See also
Source
23 September 2026
This documentation was generated with AI (Claude) from the library's source code.