How to synchronise Angular2 http get?

Question

I understand using observable I can execute a method when the request is completed, but how can i wait till a http get is completed and return the response using in ng2 http

Answer 1

How about to use $.ajax(of jQuery) or XMLHttpRequest.

It can use as asynchornize.

Answer 2

Another solution would be to implement a priority queue of sort.

From what I understand http requests do not get executed until you add subscribers. Therefore, you can do something like this:

Observable<Response> observable = http.get("/api/path", new RequestOptions({}));

requestPriorityQueue.add(HttpPriorityQueue.PRIORITY_HIGHEST, observable,
                 successResponse => { /* Handle code */ }, 
                 errorResponse => { /* Handle error */ });

This assumes that requestPriorityQueue is a service injected into your component. The priority queue would store entries in an array in the following format:

Array<{
    observable: Observable<Response>, 
    successCallback: Function, 
    errorCallback: Function
}>

You would have to decide how the elements are added to your array. Finally, the following will happen in the background:

// HttpPriorityQueue#processQueue() called at a set interval to automatically process queue entries

The processQueue method would do something like this:

protected processQueue() {
    if (this.queueIsBusy()) {
        return;
    }

    let entry: {} = getNextEntry();
    let observable: Observable<Response> = entry.observable;

    this.setQueueToBusy(); // Sets queue to busy and triggers an internal request timeout counter.
    observable.subscribe()
        .map(response => {
            this.setQueueToReady();
            entry.successCallback(response);
        })
        .catch(error => {
            this.setQueueToReady();
            entry.errorCallback(error);
        });
}

If you are able to add new dependencies you could try using the following NPM package: async-priority-queue