Next.js：如何在服务器端持久化数据以从页面调用访问它

Question

I have a Next.js app with a custom server (Express) that does some stuff continuously and keeps some data in memory as long as the server is alive.

I want to access this data from the API calls (pages). What is the proper way to store and access it?

My server index file:

    import { createServer } from 'http'
    import express from 'express'
    import { parse } from 'url'
    import next from 'next'
    import pinoHttp from 'pino-http'
    
    const logger = pinoHttp()
    const dev = process.env.NODE_ENV !== 'production'
    const nextApp = next({ dev })
    
    try {
      const handle = nextApp.getRequestHandler()
      const port = process.env.NODE_PORT || 3000
      
      nextApp.prepare().then(() => {
        const app = express()
        app.locals.myArray = []
        
        // Do stuff in the background that will update the array
        
        createServer((request, response) => {
          const parsedUrl = parse(request.url, true)

          logger(request, response)
          handle(request, response, parsedUrl)
        }).listen(port, (error?: Error) => {
          if (error) throw error
        
          console.log(`Listening on: http://localhost:${port}`)
        })
      })
    } catch (error) {
      console.log(error)
      process.exit(1)
    }

My page:

    import { Request, Response } from 'express'
    
    export default async function (request: Request, response: Response): Promise<void> {
      // Here, request.app and response.app are both undefined.
    }

Answer 1

If your data only needs to persist as long as your nodejs program is running you can store it in RAM using the Map object . Maps are collections of key / value pairs much like C# Dictionaries, python dictionaries, or php arrays.

You can create this object just once when you start up and then attach it to your Express app object like so.

var app = express();
app.locals.myMap = new Map()

Then, in each route handler you can refer to it like so.

const myMap = req.app.locals.myMap

Then you can write code like this:

let userdata = {}
const username = 'whatever'
if(myMap.has(username)) {
   userdata = myMap.get(username)
}
...
myMap.set(username, userdata)

This particular example stores a userdata object in the Map for each username .

Obviously the Map vanishes without a trace if your nodejs stops for whatever reason.

You can put anything you like in app.locals ; it doesn't have to be a Map.