How can i use promise that coming from another page in node.js

Question

I have 2 pages in my controller folder like this:

General.js

const Person = require('../models/person');
let personInfo = new Promise((success,reject)=>{
  Person.find({ Group: 'pre'})
    .then((par) => {
      if (par.length > 0) {
        success(par);
      } else {
        reject("Error");
      }
    })
    .catch((err) => { console.log(err); });
});
module.exports.personInfo = personInfo;

Account.js

    exports.Ac = (req, res, next) => {
    let person = new require('./general');
    person.personInfo
    .then((par) => {
      return res.render('/myPage/Account', {
        title: 'Account',
        group: par
      });
    })
    .catch((err) => { console.log(err); });
  }

Problem is , this promise working when server beginning but only once after its not working , par value always being same. If i change datas on my database , datas not changing on my web page.

Put your Promise in a function that returns it, then call this function. `const personInfo = () => new Promise(...); module.exports = personInfo` and in account.js : `personInfo().then(...)` — Jeremy Thille, Feb 24 '21 at 12:44
I really thank you its worked , i tried before this with curly braces it didn't work but i tried like your solution now its working. — Reşit Abdullah Yavuzkol, Feb 24 '21 at 12:56
Cool, you're welcome. If you use curly braces you need to add `return` — Jeremy Thille, Feb 24 '21 at 12:58

Mulan · Accepted Answer · 2021-02-24T13:05:54.157

anti-pattern

This is the explicit promise construction anti-pattern -

let personInfo = new Promise((success,reject)=>{
  Person.find({ Group: 'pre'})
    .then((par) => {
      if (par.length > 0) {
        success(par);
      } else {
        reject("Error");
      }
    })
    .catch((err) => { console.log(err); });
});

You can replace it with -

let personInfo = Person.find({ Group: 'pre'})
  .then((par) => {
    if (par.length > 0) {
      return par
      } else {
        throw Error("Error: empty par");
      }
    })
  .catch(console.error)  // <- don't catch here

And you should probably leave the .catch off and expect the caller to handle error handling. The .catch handler below would never trigger if the error is catch'd before

exports.Ac = (req, res, next) => {
  let person = new require('./general');
  person.personInfo
    .then((par) => {
      res.render('/myPage/Account', {  // no "return" needed
        title: 'Account',
        group: par
      });
    })
    .catch((err) => { console.log(err); }); // <- keep catch here
}

The reason it is only happening once, is because Promises can only be resolved or rejected once. You'll have to replace personInfo with a function -

const Person = require('../models/person');

const fetchPersonInfo = () =>
  Person.find({ Group: 'pre'})
    .then((par) => {
      if (par.length > 0) {
        return par
      } else {
        throw Error("Error: empty par");
      }
    })
});

module.exports.fetchPersonInfo = fetchPersonInfo;

async await

You might also want to consider reading up on async/await as they make your life a lot better

const Person = require('../models/person');

async function fetchPersonInfo () {              // <- async
  const par = await Person.find({ Group: 'pre'}) // <- await
  if (par.length > 0)
    return par;
  else
    throw Error("Error: empty par");
});

module.exports.fetchPersonInfo = fetchPersonInfo;

const { fetchPersonInfo } = new require('./general');  // <- top-level import

exports.Ac = async (req, res, next) => {  // <- async
  try {
    const par = await fetchPersonInfo()   // <- await
    res.render('/myPage/Account', {
      title: 'Account',
      group: par
    });
  } catch (err) {
    console.log(err)
  }
}

How can i use promise that coming from another page in node.js

1 Answers1