add mongodb demo

.gitignore

@@ -1,6 +1,6 @@
 .DS_Store
 *.swp
 .vscode/
-node_module
+node_modules
 package*.*
 *.db

src/database/mongodb/demo/demo.js

@@ -0,0 +1,59 @@
+const MongoClient = require('mongodb').MongoClient
+const url = 'mongodb://root:to0r@localhost:27017'
+const dbName = 'user'
+const collectionName = 'user'
+
+MongoClient.connect(url, {useUnifiedTopology: true}, async function(err, client) {
+  // create database
+  const db = client.db(dbName)
+  // create collection named user
+  const user = await Promise.resolve(db.createCollection(collectionName))
+
+  // insert data
+  user.insertOne({
+    name: 'Alice'
+  }, function(err, res) {
+    if (err) {
+      return console.log('insert fail', err)
+    }
+    console.log('insert data: ', res.result)
+  })
+
+  // find
+  user.find({
+    name: 'Alice'
+  }).toArray(function(err, result) {
+    console.log('find Alice: ', result)
+  })
+
+  // update
+  user.updateOne({
+    name: 'Alice'
+  }, {
+    $set: {
+      age: 20
+    }
+  }, function(err, res) {
+    if (err) {
+      return console.log(err)
+    }
+    console.log('update Alice data')
+  })
+
+  // find update
+  user.find({
+    name: 'Alice'
+  }).toArray(function(err, result) {
+    console.log('find Alice new data: ', result)
+  })
+
+  // delete
+  user.deleteOne({
+    name: 'Alice'
+  }, function(err, obj) {
+    if (err) {
+      return console.log(err)
+    }
+    console.log('remove data')
+  })
+})