JavaScript for loop not executed although valid array provided

Question

Trouble finding the reason why JavaScript for loop is not executing. Wrote 2 simple functions below that I want to execute and run i.e.: Bought method should try to "simulate" synchronous code. The problem is that for some reason the for loop in the addNodes() method is never executed. However, if I run this separately i.e. for example line by line

var result = [];
var addressBookNodes = await generateAddressBooksNodes();
addNodes(result, addressBookNodes);

that tells me that the code is running fine however most likely it has something to do with the asynchronous nature of the generateAddressBooksNodes method. If I simply run the command :

var addressBookNodes = await generateAddressBooksNodes();

in the browser, I get an array of objects exactly what I was expecting to get. Basically the generateAddressBooksNodes returns a promise and when that promise is resolved I can see the correct array returned however what I do not understand why the for loop is not executed if the nodes objects have at least one element as shown in the picture below.

function addNodes(result, nodes){
    console.log("3");
    console.log(nodes);
    for (var num in nodes) {
        console.log("4");   
        let singleNode = nodes[num];
        console.log(singleNode);        
        console.log("5");
        result.push(singleNode);
    }
}

async function getAddressBookAndContactNodes() {  
    var result = [];
    console.log("1");
    var addressBookNodesPromise = generateAddressBooksNodes();
    addressBookNodesPromise.then( (arrayOfAddressBookNodes) => {
        console.log("2");
        addNodes(result, arrayOfAddressBookNodes);          
    })      
    return result;  
}

Update 26 August 2020 :

After poking around the "arrayOfAddressBookNodes" object i noticed something really strange. I added additional print statement and printed the length of the "arrayOfAddressBookNodes" array. The length of the array is 0 when runned in the function. I do not understand how the length can be 0 if the object is printed shortly before the for loop and as shown on the picture below the length there is :1. What the hell is going on here?

I found another article i.e. JavaScript Array.length returning 0 that is basically explaining this. And in one of the commends it has been mentioned to use Map instead of an Array. I decided to use Set, and still get the same error i.e. the size of the set is 0 although the Set contains an object. i.e. below is the code and the picture of that execution.

  async function getAddressBookAndContactNodes() {
    var result = new Set();
    console.log("1");
    var addressBookNodes = await generateAddressBooksNodes();
    console.log("2");
    console.log(addressBookNodes);
    console.log("3");
    console.log("addressBookNodes size : " + addressBookNodes.size);
    addressBookNodes.forEach(function(value) {
        result.add(value);
    });
    console.log("6");
    console.log(result);
    console.log("7");
    return result;
}

example using set

all this is really confusing to someone having a c++ backgroud, it makes my head explode.

Update 2 : 26 August 2020. Ok i solved my problem. The problem was that the the promises are not working withing the for loop everything is explained here.

i need to use the regular "for (index = 0; index < contactsArray.length; ++index) " instead of foreach. after that it all worked. Somehow this leaves the impression that the tools of the language are broken in so many ways.

Answer 1

If generateAddressBooksNodes is returning a promise, you can use async to wait for the results:

async function getAddressBookAndContactNodes() {

    var result = [];
    console.log("1");
    var addressBookNodesPromise = await generateAddressBooksNodes();
    // note await here. Also, unless you're using this at a later time in your code, you can save space by not assigning it to a variable and simply returning generateAddressBooksNodes
    
    addNodes(result, arrayOfAddressBookNodes);
    return result;
}