Unexpected Ordering of Knockout Observable Array

Question

Unexpected Ordering of Knockout Observable Array

Background: In my current project, I am engrossed in developing a user interface powered by Knockout. While I have some experience with Knockout, one particular challenge has left me puzzled. My objective is to sort an observable array named Actions and bind it to a foreach loop within a custom template. To achieve this, I have created a computed function that invokes the sort method on the Actions array.

Code:

self.Actions = ko.observableArray([]);

self.SortedActions = ko.computed(function() {
return self.Actions()
    .sort(function (a, b) {
        var aOrder = Number(a.Order());
        var bOrder = Number(b.Order());

        return aOrder < bOrder ? 1 : -1;
    });
});

<div class="row" data-bind="template: { name: 'action-template', foreach: SortedActions }"></div>

Expected Result: The goal is to arrange the array based on the Order attribute present in each action item, progressing from 1 to n. Being certain that no two orders are the same, I expect all numbers to be whole, starting from 1 and ending at n.

Actual Result: Up to a point where there are fewer than 10 actions, everything seems to be functioning correctly. However, once the number of actions exceeds 10, the order displayed does not align with my expectations. Despite consistently displaying the same sequence upon each reload, the order appears incorrect and seemingly arbitrary. There is no noticeable pattern observed, such as alphabetical sorting.

If anyone can provide insights into why this anomaly is occurring, I would greatly appreciate it. This behavior of the sort function is entirely unfamiliar to me and has me completely baffled. Feel free to ask for further information if needed. As this is my debut post, I might have made mistakes along the way.

Thanks, :)

javascript arrays sorting knockout.js data-binding

Answer 1

Answer №1

If you want to automatically sort the initial array when the observable changes, you can use a subscribe function in this way.

It's important to note that sorting for every change can be inefficient if you are adding multiple items at once to the observable. In that case, it would be better to add items to the underlying array and then call valueHasMutated().

However, if you find yourself doing this frequently, it might be clearer to just manually call the sort method on the array when needed.

var viewModel = function(){
  var self = this;
  self.Actions = ko.observableArray(["one", "two", "three"]);

  self.Actions.subscribe(function() {
    console.log("sorting ...");
    self.Actions().sort();
  });
  
  // trigger sorting
  self.Actions.push("zero");
  
  self.addnew = function(){
    self.Actions.push("new" + self.Actions().length);
  }
}

ko.applyBindings(new viewModel());

<script src="https://cdnjs.cloudflare.com/ajax/libs/knockout/3.2.0/knockout-min.js"></script>

<ol data-bind="foreach: Actions">
  <li data-bind="text: $data"></li>
</ol>

<button data-bind="click: addnew">Add new</button>

Answer 2

If you want to automatically sort the initial array when the observable changes, you can use a subscribe function in this way.

It's important to note that sorting for every change can be inefficient if you are adding multiple items at once to the observable. In that case, it would be better to add items to the underlying array and then call valueHasMutated().

However, if you find yourself doing this frequently, it might be clearer to just manually call the sort method on the array when needed.

var viewModel = function(){
  var self = this;
  self.Actions = ko.observableArray(["one", "two", "three"]);

  self.Actions.subscribe(function() {
    console.log("sorting ...");
    self.Actions().sort();
  });
  
  // trigger sorting
  self.Actions.push("zero");
  
  self.addnew = function(){
    self.Actions.push("new" + self.Actions().length);
  }
}

ko.applyBindings(new viewModel());

<script src="https://cdnjs.cloudflare.com/ajax/libs/knockout/3.2.0/knockout-min.js"></script>

<ol data-bind="foreach: Actions">
  <li data-bind="text: $data"></li>
</ol>

<button data-bind="click: addnew">Add new</button>

Unexpected Ordering of Knockout Observable Array

Answer №1

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