promise.js

const fileNames = ['one.js', 'two.scss', 'three.scss'];

const getAllFileNames = () => new Promise((resolve, reject) => { resolve(fileNames) })

const filterScssFiles = (fileNames) => new Promise((resolve, reject) => resolve(fileNames.filter(fileName => fileName.endsWith('.scss'))))

getAllFileNames().then(fileNames => filterScssFiles(fileNames))
    .then(scssFileNames => console.log(scssFileNames))
    .catch(err => console.error(err))