Node.js running two functions in parallel

Question

I need to run two tasks in parallel in Node.js like how we spawn two threads in Java. I looked though all of the documentation related to promises and async/await.

I went through the following threads:

1. Parallel function calls in Node.js
2. Parallel operations with Promise.all?

Even if I use Promise.all, the code is getting executed sequentially.

I couldn't find a way to do so. I see that HTTP.get executes in the background, and once the results are available, it returns the response in callback. Until that happens, my program can perform other tasks. Can I do something like this to accomplish parallelism in my own code?

I have the following code. I want to make sure that func1 and func2 run in parallel.

I am expecting an output in the following order:

calling func1
calling func2
called all functions
promise 1 done!
promise 2 done!

This is my code

function func1() {

  let promise = new Promise((resolve, reject) => {
    try {
    for(var q=0;q<10000;q++) {
        console.log(q);
    }
    resolve("promise 1 done!")
    } catch(e) {
    reject(e);
    }
  });
  return promise;
}

function func2() {

  let promise = new Promise((resolve, reject) => {
    try {
    for(var r=0;r<10000;r++) {
        console.log(r);
    }
    resolve("promise 2 done!")
    } catch(e) {
    reject(e);
    }
  });
  return promise;
}


function func() {
    console.log("calling func1");
    var promise1 = func1();

    console.log("calling func2");
    var promise2 = func2();

    console.log("called all functions");
    //do some other task

    promise1
.then(result => { console.log("Promise 1 : "+result); })
.catch(error => { console.log("Promise 1 err : "+error ); });

    promise2
.then(result => { console.log("Promise 2 : "+result); })
.catch(error => { console.log("Promise 2 err : "+error ); });
}

func();
                                                                                                                                                                                                    

In short, how can I make the two for loops execute in parallel? Is it possible in Node JS or am I missing something?

Answer 1

You can use Promise.all. Example:

var promise1 = func1();
var promise2 = func2();

Promise.all([promise1, promise2])
  .then(results => console.log(results)); // [promise1Result, promise2Result]

If you want promises to resolve one after the other you can do:

func1().then(result1 => {
  // do something with the result
  return func2();
})
.then(result2 => {
  // do something with the result
})
.catch(err => console.log(err));