how to override express-session destroy method Nodejs - node.js

Question

I am working on a project that need to be notified when session destroy is called Or other alternative is that overriding destroy method of the session and implement my codes there. Anyone knows how can we do that ?
I have tried to understand express-session code at
https://github.com/konteck/express-sessions
but I could not get how can I do that yet. Also in some part of codes he uses
for (var i in MongoStore) {
SessionStore.prototype[i] = MongoStore[i];
}
which to me it is the first time that I see prototype array form like that and have no idea what does it mean (I almost know about prototype but not in this form) Anyone has any explanation from this code?
Thanks
var express = require('express');
var mongoose = require('mongoose');
var redis = require("redis");
var MongoStore = {
client: null,
options: {},
get: function (sid, cb) {
MongoStore.client.findOne({sid: sid}, function (err, doc) {
try {
if (err) return cb(err, null);
if (!doc) return cb();
cb(null, doc.data); // JSON.parse(doc.data)
}
catch (err) {
cb(err);
}
});
},
set: function (sid, data, cb) {
try {
var lastAccess = new Date();
var expires = lastAccess.setDate(lastAccess.getDate() + 1);
if (typeof data.cookie != 'undefined') {
expires = data.cookie._expires;
}
if (typeof data.lastAccess != 'undefined') {
lastAccess = new Date(data.lastAccess);
}
MongoStore.client.findOneAndUpdate({sid: sid}, {
data: JSON.parse(JSON.stringify(data)), //JSON.stringify(data)
lastAccess: lastAccess,
expires: expires
}, { upsert: true }, cb);
}
catch (err) {
console.log('express-sessions', err);
cb && cb(err);
}
},
destroy: function (sid, cb) {
MongoStore.client.remove({ sid: sid }, cb);
},
all: function (cb) {
MongoStore.client.find(function (err, doc) {
if (err) {
return cb && cb(err);
}
cb && cb(null, doc);
});
},
length: function (cb) {
MongoStore.client.count(function (err, count) {
if (err) {
return cb && cb(err);
}
cb && cb(null, count);
});
},
clear: function (cb) {
MongoStore.client.drop(function () {
if (err) {
return cb && cb(err);
}
cb && cb();
});
}
}
var RedisStore = {
client: null,
options: {},
get: function (sid, cb) {
RedisStore.client.get(RedisStore.options.collection + ':' + sid, function (err, doc) {
try {
if (err) return cb(err, null);
if (!doc) return cb();
cb(null, JSON.parse(doc)); // JSON.parse(doc.data)
}
catch (err) {
cb(err);
}
});
},
set: function (sid, data, cb) {
try {
var lastAccess = new Date();
var expires = lastAccess.setDate(lastAccess.getDate() + 1);
if (typeof data.cookie != 'undefined') {
expires = data.cookie._expires;
}
if (typeof data.lastAccess != 'undefined') {
lastAccess = new Date(data.lastAccess);
}
RedisStore.client.set(RedisStore.options.collection + ':' + sid, JSON.stringify(data), cb);
if (RedisStore.options.expire) {
RedisStore.client.expire(RedisStore.options.collection + ':' + sid, parseInt(RedisStore.options.expire));
}
}
catch (err) {
console.log('express-sessions', err);
cb && cb(err);
}
},
destroy: function (sid, cb) {
RedisStore.client.del(RedisStore.options.collection + ':' + sid, cb);
},
all: function (cb) {
RedisStore.client.keys(RedisStore.options.collection + ':*', function (err, docs) {
if (err) {
return cb && cb(err);
}
cb && cb(null, docs);
});
},
length: function (cb) {
RedisStore.client.keys(RedisStore.options.collection + ':*', function (err, docs) {
if (err) {
return cb && cb(err);
}
cb && cb(null, docs.length);
});
},
clear: function (cb) {
RedisStore.client.del(RedisStore.options.collection + ':*', cb);
}
}
var SessionStore = function (options, cb) {
var options = {
storage: options.storage || 'mongodb',
host: options.host || 'localhost',
port: options.port || (options.storage == 'redis' ? 6379 : 27017),
db: options.db || 'test',
collection: options.collection || 'sessions',
instance: options.instance || null,
expire: options.expire || 86400
};
express.session.Store.call(this, options);
switch (options.storage) {
case 'mongodb':
if (options.instance) {
mongoose = options.instance;
} else {
mongoose.connect('mongodb://' + options.host + ':' + options.port + '/' + options.db);
}
var schema = new mongoose.Schema({
sid: { type: String, required: true, unique: true },
data: { type: {} },
lastAccess: { type: Date, index: { expires: parseInt(options.expire) * 1000} },
expires: { type: Date, index: true }
});
MongoStore.options = options;
MongoStore.client = mongoose.model(options.collection, schema);
for (var i in MongoStore) {
SessionStore.prototype[i] = MongoStore[i];
}
break;
case 'redis':
if (options.instance) {
RedisStore.client = options.instance;
} else {
RedisStore.client = redis.createClient(options.port, options.host);
}
RedisStore.options = options;
for (var i in RedisStore) {
SessionStore.prototype[i] = RedisStore[i];
}
break;
}
if (cb) cb.call(null);
}
SessionStore.prototype = new express.session.Store();
module.exports = SessionStore;