A express.js middleware can automatically record user information in LINE messages API nodejs-sdk. This logger will be triggered by user with following event and unfollowing event.

(When user unfollows your bot, DB will clean his or her data.)

Run mongoDB service in docker and make sure it run at project root directory:

docker run --rm -d --name mongo -p 27017:27017 -v $PWD/db_data:/data/db mongo

Install middleware:

npm install line-express-userlogger --save

In line-bot-sdk-nodejs, you can use webhook as below:

app.post('/webhook', line.middleware(config), (req, res) => {
    //something...
});

Now, you just need to add userlogger in middleware:

const userlogger = require('line-express-userlogger')
app.post('/webhook', line.middleware(config), userlogger, (req, res) => {
    //something...
});

When express.js server start, make sure Connected to MongoDB string showing in console.

In mongoDB shell:

>use line

switched to db line

>db.users.find({}).pretty()

{
	"_id" : ObjectId("5ed5ebcd77dc52b3a3b3d972"),
	"userId" : "U364xxx......",
	"type" : "user",
	"timestamp" : 1591077837810,
	"__v" : 0
}