Nodejs: Leia e Escreva Arquivo: Use FS e Promise

const { readFile, writeFile} = require('fs').promises;

const start = async () => {
    try {
        const first = await readFile('./content/first.txt', 'utf8');
        const second = await readFile('./content/second.txt', 'utf8');

        // Write file
        await writeFile('./content/result_mind_grenade.txt', `THIS IS AWESOME : ${first}  ${second}`, { flag: 'a' });
        
        console.log(first); 
        console.log(second);
    } catch (error) {
        console.log(error);
    }
}

start();

Sore Sardine