readFile async await in nodejs

Question

import http from "http"
import fs from "fs"

function readDemo(path){
    return new Promise((resolve,reject)=>{
        fs.readFile(path,(err,data)=>{
            if(err)
                reject(err);
            else
                resolve(data);
        })
    })
}

const server = http.createServer((req,res)=>{
    if(req.url === `/`){
        res.writeHead(200,{"Content-type":"text/html"});
        readDemo(`./todo.html`)//
            .then(data => res.write(data))
            .catch(console.log);
        res.end();
    }
})

server.listen(5000);

I'm trying to load todo.html by requesting localhost:5000 as running my own server in Nodejs
It seems fs.readFile took long time to load css and javascript section so I made Promise statement to make res.write waiting for fs.readFile to finish load todo.html include css and javascript linked in it.

However code set err says

events.js:292
      throw er; // Unhandled 'error' event
      ^

Error [ERR_STREAM_WRITE_AFTER_END]: write after end
    at writeAfterEnd (_http_outgoing.js:668:15)
    at write_ (_http_outgoing.js:680:5)
    at ServerResponse.write (_http_outgoing.js:661:15)
    at file:///C:/Users/KUSW-14/Downloads/web_study-main/web_study-main/to_do_list/main.js:19:31   
Emitted 'error' event on ServerResponse instance at:
    at writeAfterEndNT (_http_outgoing.js:727:7)
    at processTicksAndRejections (internal/process/task_queues.js:81:21) {
  code: 'ERR_STREAM_WRITE_AFTER_END'
}

Can anyone help me what's wrong with my code?

fyi fs.promises.readFile

Matt
– Matt

2021-01-11 08:22:18 +00:00
Commented Jan 11, 2021 at 8:22 — Matt
– Matt, Commented Jan 11, 2021 at 8:22

jfriend00 · Accepted Answer · 2021-01-11 08:07:34Z

The readFile() is non-blocking so you're calling res.end() BEFORE you call res.write(). I'd suggest using await like this:

const server = http.createServer(async (req, res) => {
    if(req.url === `/`){
        try {
            const data = await readDemo(`./todo.html`);
            res.writeHead(200,{"Content-type":"text/html"});
            res.write(data)
            res.end();
        } catch(e) {
            console.log(e);
            res.writeHead(500);
            res.end();
        }
    } else {
        res.writeHead(404);
        res.end();
    }
});

Without await, you need to move the res.end() inside of the .then():

const server = http.createServer((req,res)=>{
    if(req.url === `/`){
        readDemo(`./todo.html`).then(data => {
            res.writeHead(200,{"Content-type":"text/html"});
            res.write(data);
            res.end();
        }).catch(err => {
            console.log(err);
            res.writeHead(500);
            res.end();
        });
    } else {
        res.writeHead(404);
        res.end();
    }
});

FYI, in modern versions of node.js fs.promises.readFile() is already a promise version so you don't have to make your own.

Collectives™ on Stack Overflow

readFile async await in nodejs

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related