How can I stop an object method call before the ajax has completed

I have a the following java script object

function eventTypeObj() {

allEventTypes = [];

// When the object is created go and get all the e开发者_运维技巧vent types that can be included in journey or clusters.
$.ajax({
        url: "/ATOMWebService.svc/GetDisplayEventTypes",
        dataType: "json",
        success: function(result) {
            allEventTypes = eval("(" + result.d + ")");
        }
    });


// Returns a list of all the event type IDS.
this.getEventTypeIds = function() {
    var eventTypeIDs = [];
    for (var i = 0; i < allEventTypes.length; i++) {
        eventTypeIDs.push(allEventTypes[i].Id);
    }
    return eventTypeIDs;
};
}

I was wondering if there is a way stop some one calling the eventTypeObj.getEventTypeIds(); before the ajax call in the constructor has succeeded, and there is no data in the allEventTypes array?

Something like this would be way better (im not guaranteeing this is 100% working, but the concept is sound):

function eventTypeObj() {
    this.allEventTypes = [];
    this.hasLoadedEventTypes = false;

    var loadEventTypes = function(cb) {
        $.ajax({
            url: "/ATOMWebService.svc/GetDisplayEventTypes",
            dataType: "json",
            success: function(result) {
                this.allEventTypes = eval("(" + result.d + ")");
                this.hasLoadedEventTypes = true;
                cb();
            }
        });
    };


    this.getEventTypeIds = function(updateEventTypes, callback) {
        var _getEventTypeIds = function() {
            var eventTypeIDs = [];
            for (var i = 0; i < this.allEventTypes.length; i++) {
                eventTypeIDs.push(this.allEventTypes[i].Id);
            }    
            return eventTypeIDs;
        };


        if (!this.hasLoadedEventTypes || updateEventTypes) {
            loadEventTypes(function(){ callback(_getEventTypeIds()); });
        }
        else callback(_getEventTypeIds());
    };
}

Example usage:

var eto = new eventTypeObj();

eto.getEventTypeIds(false, function(eventTypeIdArray) {
   // do stuff with the id array 
});


/*
    somewhere later on you want to get an updated eventTypeId array
    in case the event types have changed.
*/
eto.getEventTypeIds(true, function(eventTypeIdArray) {
    // do stuff with the updated ids
});

var allowCall = false;
function eventTypeObj() {

allEventTypes = [];

// When the object is created go and get all the event types that can be included in journey or clusters.
$.ajax({
        url: "/ATOMWebService.svc/GetDisplayEventTypes",
        dataType: "json",
        success: function(result) {
            allEventTypes = eval("(" + result.d + ")");
            allowCall = true;
        }
    });


// Returns a list of all the event type IDS.
this.getEventTypeIds = function() {
    if(!allowCall) return;  // or pop up a message
    var eventTypeIDs = [];
    for (var i = 0; i < allEventTypes.length; i++) {
        eventTypeIDs.push(allEventTypes[i].Id);
    }
    return eventTypeIDs;
};
}

Or just check if allEventTypes is empty or not.

There is no way to prevent someone from calling it too soon. What would you want to have happen if they call it too soon?

It looks like your code now currently returns an empty array if allEventTypes hasn't yet been filled in. You can decide whether the empty array is the right result or if you should throw an exception when it's called too early to make it absolutely clear to the caller that the data is not yet available.

You could provide some helper code for people who need that information, but it might not yet be available. For example, you could allow them to register a callback that would get called from the success handler after the data had been filled in. You could allow them to query whether the data is available yet.

If you don't want the responsibility for the timing to be on the callers, then you cannot offer a synchronous way to get this information. Instead, you would only offer a callback mechanism for getting the data. If the data is ready, the callback would get called immediately. If the data is not ready, the callback would get called when the ajax function completes. In either case, the caller would have to process the data in the callback only and getEventTypeIds would not be a normal call to get the data like it is now, but rather a call to register a callback that would be called with the data when was ready. This would relieve the caller from having to know implementation details of when the data was ready, but would force them to use the asynchronous nature of the callback mechanism.

this.getEventTypeIds = function(callback) {
    if (allEventTypes.length > 0) {
        // data is ready call the callback with the data now
    } else {
        // store the callback to be called later from the success handler
    }
}

You can check if the eventType array is empty, right?

if(allEventTypes.length == 0)
{
    return;
}