Check a folder for changed files in NodeJS

index.js

// Run at least once. Directory is the directory to check, Datapath should point to a json file with an empty array (`[]`) where Node can store file data

function checkForChangedFiles(directory, datapath) {
    return new Promise(resolve => {
        let filedata = require(datapath);
        let changedfiles = [];
        fs.readdir(directory, async (err, files) => {
            if (err) throw new Error('Unabled to check for existing files. Reason: readdir failed. \n' + err);
            for (let i in files) {
                if ((function() {
                    for (let o = filedata.length - 1; o > -1; o--) {
                        if (filedata[o].name === files[i]) return true;
                    }
                })() && files[i] !== 'node_modules') {
                    console.log('Found existing file data: ' + files[i]);
                    for (let o in filedata) {
                        if (filedata[o].name == files[i]) {
                            if (filedata[o].size !== fs.statSync(directory + '\\' + files[i]).size) {
                                console.log(files[i] + ' has changed');
                                changedfiles.push(files[i]);
                                filedata.splice(o);
                                filedata.push({
                                    "name": files[i],
                                    "size": fs.statSync(directory + '\\' + files[i]).size
                                });
                                fs.writeFileSync(datapath, JSON.stringify(filedata), undefined, err => {
                                    if (err) throw new Error('Unable to save file data. Reason: writeFileSync failed. \n' + err);
                                    filedata = require(datapath);
                                });
                            }
                        }
                    }
                } else if (files[i] !== 'node_modules') {
                    changedfiles.push(files[i]);
                    console.log('File not registered. Saving data...');
                    filedata.push({
                        "name": files[i],
                        "size": fs.statSync(directory + '\\' + files[i]).size
                    });
                    fs.writeFileSync(datapath, JSON.stringify(filedata), undefined, err => {
                        if (err) throw new Error('Unable to save file data. Reason: writeFileSync failed. \n' + err);
                        filedata = require(datapath);
                    });
                }
            }
            resolve(changedfiles);
        });
    });
}