electron/lib/browser/api/session.js

const bindings = process.atomBinding('session')
const PERSIST_PREFIX = 'persist:'

// Returns the Session from |partition| string.
exports.fromPartition = function (partition) {
  if (partition == null) {
    partition = ''
  }
  if (partition === '') {
    return exports.defaultSession
  }
  if (partition.startsWith(PERSIST_PREFIX)) {
    return bindings.fromPartition(partition.substr(PERSIST_PREFIX.length), false)
  } else {
    return bindings.fromPartition(partition, true)
  }
}

// Returns the default session.
Object.defineProperty(exports, 'defaultSession', {
  enumerable: true,
  get: function () {
    return bindings.fromPartition('', false)
  }
})