Walk directory for files in nodejs

directory_walker.js

const fs = require('fs'),
    path = require('path'),
    fs_promise = fs.promises;

async function walk(dir) {
    let files = await fs_promise.readdir(dir);
    files = await Promise.all(files.map(async file => {
        let filePath = path.join(dir, file);
        let stats = await fs_promise.stat(filePath);

        if (stats.isDirectory()) {
            return walk(filePath);
        }
        else if(stats.isFile()) {
            return filePath;
        }
    }));

    return files.reduce((all, folderContents) => all.concat(folderContents), []);
}

//example usage
walk(directory).then(function(files){
  files.sort();
});