isPrimitiveType function const isBoolean = (variable) => typeof variable === 'boolean' const isString = (variable) => typeof variable === 'string' const isNumber = (variable) => typeof variable === 'number' const isUndefined = (variable) => typeof variable === 'undefined' // typeof null === 'object' due to historical reason const isNull = (variable) => variable === null const isSymbol = (variable) => typeof variable === 'symbol' const isBigint = (variable) => typeof variable === 'bigint' Example isBoolean(true) // true isString('str') // true isNumber(666) // true isUndefined(undefined) // true isSymbol(Symbol('foo')) // true isBigint(9007199254740991n) // true isNull(null) // true