How do you read and write session variables in Express.js?

Treat req.session as a plain object whose properties persist across requests for the same session.

Setting a value:

function (req, res) {
  req.session.lastOption = 4;
}

Reading a value:

function (req, res) {
  if (req.session.hasOwnProperty('lastOption')) {
    let value = req.session.lastOption;
  }
}

Session variables persist across requests for the same session.