Javascript - synchronizing after asynchronous calls

Question

I have a Javascript object that requires 2 calls out to an external server to build its contents and do anything meaningful. The object is built such that instantiating an inst

Answer 1

That's some good stuff Mr. Kyle.

To put it a bit simpler, I usually use a Start and a Done function.
-The Start function takes a list of functions that will be executed.
-The Done function gets called by the callbacks of your functions that you passed to the start method.
-Additionally, you can pass a function, or list of functions to the done method that will be executed when the last callback completes.

The declarations look like this.

var PendingRequests = 0;
function Start(Requests) {
    PendingRequests = Requests.length;
    for (var i = 0; i < Requests.length; i++)
        Requests[i]();
};
//Called when async responses complete. 
function Done(CompletedEvents) {
PendingRequests--;
    if (PendingRequests == 0) {
        for (var i = 0; i < CompletedEvents.length; i++)
            CompletedEvents[i]();
    }
}

Here's a simple example using the google maps api.

//Variables
var originAddress = "*Some address/zip code here*"; //Location A
var formattedAddress; //Formatted address of Location B
var distance; //Distance between A and B
var location; //Location B

//This is the start function above. Passing an array of two functions defined below.
Start(new Array(GetPlaceDetails, GetDistances));


//This function makes a request to get detailed information on a place. 
//Then callsback with the **GetPlaceDetailsComplete** function
function GetPlaceDetails() {
    var request = {
        reference: location.reference //Google maps reference id
    };
    var PlacesService = new google.maps.places.PlacesService(Map);
    PlacesService.getDetails(request, GetPlaceDetailsComplete);
}

function GetPlaceDetailsComplete(place, status) {
    if (status == google.maps.places.PlacesServiceStatus.OK) {
        formattedAddress = place.formatted_address;
        Done(new Array(PrintDetails));
    }
}


function GetDistances() {
    distService = new google.maps.DistanceMatrixService();
    distService.getDistanceMatrix(
    {
        origins: originAddress, 
        destinations: [location.geometry.location], //Location contains lat and lng
        travelMode: google.maps.TravelMode.DRIVING,
        unitSystem: google.maps.UnitSystem.IMPERIAL,
        avoidHighways: false,
        avoidTolls: false
    }, GetDistancesComplete);
}
function GetDistancesComplete(results, status) {
    if (status == google.maps.DistanceMatrixStatus.OK) {
        distance = results[0].distance.text;
        Done(new Array(PrintDetails));
    }
}

function PrintDetails() {
    alert(*Whatever you feel like printing.*);
}

So in a nutshell, what we're doing here is
-Passing an array of functions to the Start function
-The Start function calls the functions in the array and sets the number of PendingRequests
-In the callbacks for our pending requests, we call the Done function -The Done function takes an array of functions
-The Done function decrements the PendingRequests counter
-If their are no more pending requests, we call the functions passed to the Done function

That's a simple, but practicle example of sychronizing web calls. I tried to use an example of something that's widely used, so I went with the Google maps api. I hope someone finds this useful.