Javascript Asynchronous Order

Question

My question is specific to Javascript and asynchronous operations. I am building a Node.js API for interacting with a database (OrientDB) and I am using a Node-orient package providing basic connectivity functions. Some of these functions look like the following:

db.delete("...")
db.insert("...")
etc.

Each of them return a promise that can be used to act on the results:

db.insert("...").then(function(records) {
    res.send(records);
});

My goal is to execute two delete statements (order does not matter) and then execute an insert statement (must happen after the delete statements else I will end up deleting the inserted record). Can I simply write the following:

db.delete("...");
db.delete("...");
db.insert("...");

In other words, is the order of aynchronous operations in a single-threaded environment like Javascript maintained??? or do I need to create some sort of promise:

var promise = new Promise(function(resolve, reject) {

    db.delete("thing to delete").then(handleFinish, reject);
    db.delete("other thing to delete").then(handleFinish, reject);

    var finished = false;

    function handleFinish() {
        if(finished){
            resolve();
        }
        else {
            finished = true;
        }
    }
});

and then

promise.then(function(){
    db.insert("...");
});

Or is there some better alternative to accomplishing this? I'm new to Node and new to asynch programming.

Answer 1

This can be achieved with promises, for which many modules exist. Here's an example with promise

var Promise = require('promise');

Promise.all([
  db.delete(...),
  db.delete(...)
]).then(function(result) {
  db.insert(...);
});

When you're dealing with callbacks, you can use a control flow module such as async