C# 异步任务 vs Js 异步任务（节点 js）

Question

Ok, so I know how to program in C# fairly well and I have started programming in JS recently (node js). To be honest I was in a bot of shock from async calls.

Let's say I have this code in C#:

var t_1 = SomeAsyncTask();
var t_2 = SomeOtherAsyncTask();
Task.WaitAll(t_1, t_2);
var res_1 = t_1.Result;
var res_2 = t_2.Result;

Is there a JS equivalent of this? So far I have managed this:

In User.js:
var express = require("express");
var router = express.Router();
var sqlDo = require("../../js_help/DatabasReq/sqlDo.js");
router.get("/", async function(req, res){
    var json = sqlDo.ExecCommand("select * from Users");
    res.send(json); //json.recordset
});
module.exports = router;

In sqlDo.js:
module.exports = {
    ExecCommand: function(command){
        // sql and config are defined before.
        sql.connect(config, function () {
            var request = new sql.Request();
            request.query(command, function (err, recordset) {
                if (err) console.log(err)
                console.log(recordset.recordset);
                return recordset;
            });
        });
    }
};

My problem is that this code is running async. I have tried putting await to different places but nothing worked. So when I start my server it returns nothing. I can tell that it is completing a call because I let it read results into console.

Thanks for any help!

Btw: I have tried googling/stackoverlow-ing,.. But I was not able to find anything that would look like C# equivalent. Is it even possible to write it like in c#? Again thanks for every answer...

Answer 1

To make your ExecCommand function async, you have to make it return a Promise. Read about Promises for instance here

module.exports = {

  ExecCommand: function(command){
    return new Promise((resolve, reject) => {  //return a Promise from the function
      sql.connect(config, function () {
        var request = new sql.Request();
        request.query(command, function (err, recordset) {
          if (err) {
            reject(err);  //if there is an error, reject the Promise
          } else {
            resolve(recordset);  //if no error, resolve the Promise with the result
          }
        });
      });
    });
  }
};

Depending on your SQL library, it may also support promises already, instead of callbacks

module.exports = {

  ExecCommand: function(command) {
     return sql.connect(config)
       .then(() => {
          return new sql.Request().query(command);
       })
  }
};

or with async/await

module.exports = {

  ExecCommand: async function(command) {
    await sql.connect(config);
    return await new sql.Request().query(command);         
  }
};

Then you can call this function in the requesthandler either like this

router.get("/", async function(req, res){
  try {
    var json = await sqlDo.ExecCommand("select * from Users");
    res.send(json); 
  catch (err) {
    console.log(err);
    res.sendStatus(500);
  }
});

or like this

router.get("/", function(req, res){
  sqlDo.ExecCommand("select * from Users")
    .then(json => { //the promise resolved
      res.send(json);
    })
    .catch(err => { //the promise rejected
      res.sendStatus(500); 
      console.log(err); 
    });
});

I prefer the second variant. But that may be just my personal opinion ...