'use strict';

const sum = (a, b) => {

if (typeof a === 'number' && typeof b === 'number') {

return [null, a + b];

}

return [new Error('a and b should be numbers')];

};

{

const x = 2;

const y = 3;

const [err, total] = sum(x, y);

if (err) console.error({ x, y, err, total });

else console.log({ x, y, err, total });

}

{

const z = 7;

const c = 'A';

const [err, res = NaN] = sum(z, c);

if (err) console.error({ z, c, err, res });

else console.log({ z, c, err, res });

}