Structuring a Knockout.js application well from the start makes it easier to maintain, scale, and debug your app. You should follow the following best practices to build a clean, modular, and efficient Knockout.js app:

1. Modularize with View Models

Split view models by feature or page

Instead of one huge view model, use a modular structure:

/js
  /viewmodels
    homeViewModel.js
    userProfileViewModel.js
    productListViewModel.js

Each module handles its own concerns and can be reused or tested independently.

2. Use Components for Reusable UI

Use ko.components.register for reusable pieces

Encapsulate UI + logic in components:

ko.components.register('user-card', {
  viewModel: function(params) {
    this.name = params.name;
  },
  template: '<div data-bind="text: name"></div>'
});

Suggested folder structure:

/components
  userCard/
    userCard.js
    userCard.html

3. Keep ViewModel “View-Only”

Don't mix data access or business logic directly in the view model.

Best:

function UserViewModel(userService) {
  this.users = ko.observableArray([]);

  this.loadUsers = async function () {
    const data = await userService.getAllUsers();
    this.users(data);
  };
}

Avoid:

this.users = ko.observableArray([]);
$.get('/api/users', data => this.users(data)); // tightly coupled

Use a service layer to fetch data.

4. Use Observables Intentionally

1. Use observable() for values that change and affect the view.
2. Use plain JS values for static or config data.
3. Avoid deeply nested observable structures.

Clean:

this.settings = {
  theme: "dark",
  notifications: true
};

5. Testing-Friendly ViewModels

Structure your view models to be testable with minimal DOM assumptions.

Best:

1. Pass dependencies via constructor
2. Avoid direct DOM access
3. Use ko.isObservable() to confirm observables

Use tools like Jasmine or Mocha for testing.

6. Use Custom Bindings Wisely

Use ko.bindingHandlers to extend functionality, like tooltips, date pickers, etc.

Clean example:

ko.bindingHandlers.tooltip = {
  init: function (element, valueAccessor) {
    $(element).tooltip({ title: ko.unwrap(valueAccessor()) });
  }
};

Wrap third-party plugins here to keep your view models free of jQuery or plugin-specific code.

7. Dispose and Cleanup

1. Use ko.utils.domNodeDisposal.addDisposeCallback
2. Call .dispose() on subscriptions and computed observables
3. Clean up DOM plugin instances in custom bindings

8. Use Templates for UI Logic Separation

Organize templates in .html files (when using bundlers or frameworks), or script tags:

<script type="text/html" id="user-template">
  <div data-bind="text: name"></div>
</script>

Bind via:

<div data-bind="template: { name: 'user-template', data: user }"></div>

9. Use Tools and Utilities

1. Knockout Context Debugger (Chrome) – Inspect $data, $parent, $root
2. ko.unwrap() – Safely access observable or plain values
3. ko.cleanNode() – To unbind from DOM if replacing dynamically

10. Example App Folder Structure

/app
  /components
    userCard/
      userCard.js
      userCard.html
  /viewmodels
    dashboard.js
    login.js
  /services
    apiService.js
  main.js
  app.html