$ npm install micro-ratelimit

const rateLimit = require('micro-ratelimit')
module.exports = rateLimit((req, res) => {
  return 'Hello world'
})

const rateLimit = require('micro-ratelimit')
// Limit example: 2 requests per 10 sec
module.exports = rateLimit({ window: 10000, limit: 2, headers: true }, (req, res) => {
  return 'Hello world'
})

function keyGenerator (req) {
  return req.headers['x-forwarded-for'] ||
    req.connection.remoteAddress ||
    req.socket.remoteAddress ||
    req.connection.socket.remoteAddress
}