Node js promise chaining issue

Question

I am trying to connect to Salesforce using node js / jsforce library and use promises. Unfortunately one of the methods is executing prior to getting connection.

i have method A : makeconnection which returns the connection i have method B : which loads data from Salesforce based on the connection reference from method A I have method C : which gets dependencies from Salesforce based on connection from method A

I would like the following order to be executed A ==> B ==> C

Unfortunately C seems to run first followed by A and B so the connection is null and it fails

roughly this is the code

let jsforce = require("jsforce");
const sfdcSoup = require("sfdc-soup");
const fs = require("fs");
let _ = require("lodash");
let trgarr = [];
let clsarr = [];
let entityarr = [];

function makeConnection() {


  return new Promise((resolve,reject) => {
     const conn = new jsforce.Connection({
          loginUrl: "https://test.salesforce.com",
          instanceUrl: "salesforce.com",
          serverUrl: "xxx",
          version: "50.0"
        });

      
        conn.login(username, password, function (err, userInfo) {
          if (err) {
            return console.error(err);
          }
      
          // console.log(conn.accessToken);
          //console.log(conn.instanceUrl);
      
          //console.log("User ID: " + userInfo.id);
          //console.log("Org ID: " + userInfo.organizationId);
          console.log("logged in");
        });  
         resolve(conn);
   });
}

function loadClasses(conn) {

  return new Promise((resolve,reject) => {
     const querystr =
     "select apiVersion,name,body from apexClass where NamespacePrefix = null";
 
   let query = conn
     .query(querystr)
     .on("record", function (rec) {
       clsarr.push(rec);
     })
     .on("end", function () {
       console.log("number of class is " + clsarr.length);
       console.log("loaded all classes");
     });  
     resolve(conn,clsarr);
  });
}

async function getDependencies(conn) {




   return new Promise((resolve,reject) => {


     let entryPoint = {
          name: "xxx",
          type: "CustomField",
          id: yyy
        };
     
     let connection = {
          token: conn.accessToken,
          url: "abc.com",
          apiVersion: "50.0"
        };

       let usageApi =  sfdcSoup.usageApi(connection, entryPoint);

        usageApi.getUsage().then((response) => {
          console.log(response.stats);
          console.log(response.csv);

        });

   });

}
async function run() {
 makeConnection().then(conn => loadClasses(conn)).then(conn=>getDependencies(conn));
}

run();

I keep getting an error that says UnhandledPromiseRejectionWarning: Error: Access token and URL are required on the connection object

The reason is connection needs to be obtained from method A and sent to Method C , which is not happening. Can you please guide where i might be wrong?

Also why is method C getting executed before A and B. why does my promise chaining not work as promised?

I am running the code in Vscode and using Node 14

Answer 1

Your 2 method have minor correction first method makeConnection, the resolve should be inside login after console.log("logged in")

And second loadClasses, the resolve should be inside 'end' event. Please check below 2 method.

function makeConnection() {
  return new Promise((resolve,reject) => {
     const conn = new jsforce.Connection({
          loginUrl: "https://test.salesforce.com",
          instanceUrl: "salesforce.com",
          serverUrl: "xxx",
          version: "50.0"
        });
      
        conn.login(username, password, function (err, userInfo) {
          if (err) {
            return console.error(err);
          }
      
          // console.log(conn.accessToken);
          //console.log(conn.instanceUrl);
      
          //console.log("User ID: " + userInfo.id);
          //console.log("Org ID: " + userInfo.organizationId);
          console.log("logged in");
          resolve(conn);
        });  
         
   });
}

function loadClasses(conn) {

  return new Promise((resolve,reject) => {
     const querystr =
     "select apiVersion,name,body from apexClass where NamespacePrefix = null";
 
     let query = conn
     .query(querystr)
     .on("record", function (rec) {
       clsarr.push(rec);
     })
     .on("end", function () {
       console.log("number of class is " + clsarr.length);
       console.log("loaded all classes");
       resolve(conn,clsarr);
     });  
     
  });
}

Answer 2

you should use promise series if methods are depending on each other if methods do not depend then you should use a promise parallel. READ MORE ABOUT PROMISE SERIES AND PARALLEL.