A toggle is a switch that has two positions: on or off. The word toggle is used in both software and hardware — for example, the caps lock and num lock keys on your keyboard are both toggles that allow you to turn specific functions on or off. Toggle is also a verb, meaning “to move or alternate between two things,” as when you toggle between screens during a video chat with two friends at once.

In a web application, a toggle is an element that can be either ‘on’ or ‘off’. A toggle can be used to control a feature’s behavior or to restrict access to features based on user permissions or roles. Toggles are especially useful when introducing new features to your users, or for implementing A/B testing.

When using a toggle in your web app, you must ensure that it is properly implemented in order to prevent unwanted side effects. For instance, if you create a toggle that has the potential to cause unwanted side effects and it is not properly implemented, your users may experience unexpected errors or even crash their browsers.

If you are building an application that supports multiple toggles, you must be careful to ensure that all of the toggles work well together. Otherwise, your application may not function as expected or it may not be possible to use all of the features you have built.

Fortunately, there are many different ways to implement a toggle. Some approaches are simpler but less dynamic, such as hardcoding the toggle configuration in source code (often by using a preprocessor’s #ifdef feature). This approach is often suitable for Ops Toggles or other types of feature flags that are not intended to be used on a live production system.

A more sophisticated way to implement a toggle is to use a feature flag management platform that allows for dynamic in-memory re-configuration of the toggle configuration. This approach requires the underlying application to be restarted in order to change the toggle state, and it can therefore be disruptive to CI/CD processes if not done correctly.

Savvy teams consider a release’s toggle configuration to be inventory which comes with a carrying cost, and they try to keep it as low as possible. As such, they often include a task on the team’s backlog to remove toggles that are no longer needed when a release version is first introduced. Some teams also put expiration dates on their toggles and will not allow them to be flipped on during a test run once they have expired. This can be an effective way to prevent accidental regressions in the future.