scratch-desktop/scripts/lib/libraries.js

const backdrops = require('scratch-gui/dist/libraries/backdrops.json');
const costumes = require('scratch-gui/dist/libraries/costumes.json');
const sounds = require('scratch-gui/dist/libraries/sounds.json');
const sprites = require('scratch-gui/dist/libraries/sprites.json');

const libraries = {
    backdrops,
    costumes,
    sounds,
    sprites
};

module.exports = libraries;