const oddOrEven = (num) => ((num % 2) === 1) ? 'odd' : 'even';

console.log(oddOrEven(1));
console.log(oddOrEven(2));

or,

const evenOrOdd = (num) => ((num % 2) === 0) ? 'even' : 'odd';

console.log(evenOrOdd(1));
console.log(evenOrOdd(2));