How do you debug and troubleshoot knockout computed observable performance issues?

1 What are computed observables?

Computed observables are a powerful feature of KnockoutJS that allow you to create dynamic and reactive expressions based on other observables. For example, you can use a computed observable to calculate the total price of a shopping cart based on the quantity and price of each item. Computed observables are automatically updated whenever their dependencies change, so you don't have to manually refresh them.

2 How to measure performance?

One of the first steps to debug and troubleshoot knockout computed observable performance issues is to measure how long it takes for your computed observables to evaluate and update. You can use the browser's built-in performance tools, such as Chrome DevTools or Firefox Developer Tools, to record and analyze the execution time and memory usage of your code. You can also use the knockout performance plugin, which adds a performance tab to your browser's developer console and shows you the number of evaluations, subscriptions, and memory allocations for each observable.

3 How to avoid unnecessary evaluations?

Unnecessary evaluations are a common cause of knockout computed observable performance issues. This can occur when your computed observables are triggered more than needed, which can be caused by having too many dependencies, using non-observable properties or functions, using global variables or external libraries, or modifying observables inside your computed observables. To prevent this, you should minimize the number and complexity of dependencies in your computed observables, use observable wrappers or pure computed observables for non-observable values or functions, use dependency detection or manual subscriptions to control when your computed observables are updated, and avoid modifying observables inside your computed observables or use peek() to access their values without triggering updates.

4 How to use deferred updates?

Another way to improve knockout computed observable performance is to use deferred updates, which delay the evaluation and notification of your computed observables until the current execution context ends. This can reduce the number of times your computed observables are updated, especially if they depend on multiple observables that change frequently. To use deferred updates, you need to enable the knockout-deferred-updates plugin, which extends the knockout library and adds a deferUpdates option to your observables and computed observables. You can set this option globally or individually, depending on your needs.

5 How to use rate limiting?

Sometimes, you may want to limit the frequency of updates for your computed observables, especially if they involve expensive or asynchronous operations, such as API calls or DOM manipulations. For example, you may want to debounce or throttle your computed observables, so that they only update after a certain amount of time or a certain number of changes. To use rate limiting, you can use the rateLimit extender, which adds a rateLimit option to your observables and computed observables. You can specify the time interval or the method of rate limiting, such as notifyWhenChangesStop or throttle.

6 How to use disposal?

Finally, you should always remember to dispose your computed observables when they are no longer needed, such as when you remove an element from the DOM or navigate away from a page. Disposing your computed observables will free up the memory and resources they use, and prevent memory leaks and performance degradation. To dispose your computed observables, you can use the dispose() method, which removes all the subscriptions and references to your computed observables. You can also use the disposeWhen or disposeWhenNodeIsRemoved options, which automatically dispose your computed observables when a certain condition is met or when a certain node is removed from the DOM.