How can I read files from directory and send as JSON to client?

You have to put serialize the Logs array into json and send it back to client

app.get('/logs',function(req,res){
    res.setHeader('Content-Type', 'application/json');
    res.send(JSON.stringify(readDirectory.readDirectory()));
});

Or

app.get('/logs',function(req,res){
    res.json(readDirectory.readDirectory());
});