service method call is not synchronous

Question

I have a class OrderServer where I am calling a service OrderService which connects to DB and fetch the data. Data gathering happens every 1-minute. OrderServer use SocketIO to communicate with the webapp. code is as follows:

export class OrderServer {
// some required fields

    constructor() {
        console.log("in OrderServer Constructor...");
        this._orderService = new OrderService();
        // some other initiations and calls
        this.listen();
    }

    private listen(): void {
        this.server.listen(this.port, () => {
        });

        this.io.on('connect', (socket: socketIo.Socket) => {
            setInterval( () => {
                let orders : Order[] = this._orderService.getNewNProcessingOrders();
                console.log("Orders : " + orders);
            },60000);});}}

I have OrderService code as well but not putting it here as it doesnt seem required right now. If need be I will put it.

The problem is there is one console log statement is in getNewNProcessingOrders(). If you have noticed there is console.log statement after calling getNewNProcessingOrders() in listen method.

I expect, Console log statement in getNewNProcessingOrders() method should execute first and then the console log statment in listen() but its other way around.

Why is this._orderService.getNewNProcessingOrders(); is not blocking? I tried finding documentation but couldnt find specific to this issue where service method calls are not blocable.

Answer 1

Because if it was blocking, your whole app would freeze, doing nothing until the server sends back the result, since everything in JavaScript is executed in a single thread.

That's why promises, observables etc. exist: to deal with asynchrony. Your service can't possibly return an array of orders. It should return an observable or a promise. or take a callback (although I wouldn't advise that).