mathjs/lib/util/boolean.js

Math.js is an extensive math library for JavaScript and Node.js. It features a flexible expression parser and offers an integrated solution to work with numbers, big numbers, complex numbers, units, and matrices.

/**
 * Test whether value is a Boolean
 * @param {*} value
 * @return {Boolean} isBoolean
 */
exports.isBoolean = function isBoolean(value) {
  return (value instanceof Boolean) || (typeof value == 'boolean');
};