get-file-size.js

const fs = require('fs');

// Function to get a file size
function getFileSize(filePath) {
    return new Promise((resolve, reject) => {
        fs.stat(filePath, (err, stats) => {
            if(err) {
                reject(err);
            } else {
                let fileSizeInBytes = stats.size;  // size in bytes
                resolve(fileSizeInBytes.toString()); // convert size to string
            }
        });
    });
}

// Usage
getFileSize('./your/file/path')
    .then(size => console.log(size))
    .catch(err => console.error(err));