Creating an AJAX request in Knockout.js

Forgive me if this question has been asked previously, as my search attempts have been unsuccessful in finding a solution. Despite consulting the knockout documentation, I still struggle to articulate my issue effectively for searching.

My situation involves 3 select lists and a Knockout view model. When a value is selected in the first list, it updates an observable in the view model. Subsequently, I need to initiate an ajax post request to send that value to the server and receive a list of values back, which will then populate an observable array in the view model, updating the other two lists accordingly.

While I am comfortable with managing observables, my dilemma lies in determining how and where to trigger the ajax call.

If I trigger it upon the change event of the first select, it often leads to a race condition where the call occurs before the view model update is complete. I could bypass using the observable altogether, but that deviates from typical Knockout practices.

An alternate approach using a custom binding for data retrieval results in redundant ajax calls, and directly embedding the retrieval within a function is impractical due to its asynchronous nature and repeated invocation.

It seems necessary to establish a mechanism that monitors an observable and initiates an ajax call without any visible interaction.

Any assistance on this matter would be greatly appreciated.

Answer №1

Responding to changes in the view model typically involves using subscriptions in knockout.

function ViewModel() {
    var self = this;

    self.someValue = ko.observable();
    self.otherValue = ko.observable();

    self.someValue.subscribe(function (newValue) {
        // Perform actions based on newValue, such as making an Ajax request.

        // assuming jQuery
        $.get("your/url", {val: newValue})
        .done(function (data) {
            self.otherValue(data);
        })
        .fail(function () {
            alert("Could not fetch value from server");
        });           
    });
}

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