exports.isString = function isString(value) { return typeof value === 'string'; }; exports.isNumber = function isNumber(value) { return typeof value === 'number'; }; exports.isBoolean = function isBoolean(value) { return typeof value === 'boolean'; }; exports.isUndefined = function isUndefined(value) { return typeof value === 'undefined'; }; exports.isObject = function isObject(value) { return typeof value === 'object' && value !== null; }; exports.isFunction = function isFunction(value) { return typeof value === 'function'; };