Avoiding side effects functions in Flutter
Published: 2023-07-11 11:49:52

When you take medicine to cure a medical problem, but that medicine makes you fat, that’s known as a side effect. If you put some bread in a toaster to make toast, but the toaster burns your house down, that’s also a side effect. Not all side effects are bad, though. If you take a business trip to Paris, you also get to see the Eiffel Tower. 

When you write a function, you know what the inputs are: the
parameters. You also know what the output is: the return value. Anything beyond that, that is, anything that affects the world outside of the function, is a side effect.

```
void hello() {
    print('Hello!');
}
```

Printing something to the console is a side effect, because it’s affecting the world outside of the function. If you wanted to rewrite your function so that there were no side effects, you could write it like this:

```
String hello() {
     return 'Hello!';
}
```

Now, there’s nothing inside the function body that affects the outside world. You’ll have to write the string to the console somewhere outside of the function.

## Understanding Side Effects:

Side effects refer to any changes that occur outside the immediate scope of a function or widget. These changes can include modifying state, making network requests, performing I/O operations, accessing databases, or interacting with external services. Side effects can lead to a loss of predictability and make it difficult to reason about the behaviour of your application. Therefore, it is crucial to employ techniques that minimise side effects and ensure your app remains reliable and maintainable.

It’s fine, and even necessary, for some functions to have side effects. But as a general rule, functions without side effects are easier to deal with and reason about. You can rely on them to do exactly what you expect because they always return the same output for any given input. These kinds of functions are also called pure functions.

**Embrace Reactive Programming:**

Reactive programming is a paradigm that focuses on managing state changes in a declarative and predictable manner. In Flutter, there are several reactive programming frameworks available, such as Provider, Riverpod, Bloc, and MobX. These frameworks allow you to separate business logic from the UI, enabling better management of side effects. By encapsulating side effects within specific components, you can ensure that changes are isolated and predictable.

**Choose the Right State Management Approach:**

Selecting an appropriate state management approach can significantly reduce the occurrence of side effects. Flutter offers various state management libraries, each with its own strengths and advantages. Libraries like Provider and Riverpod encourage the use of immutable data structures and enforce unidirectional data flow. By adhering to these principles, you can prevent unintended side effects and enhance the predictability of your application.

**Utilize Async/Await and Futures:**

Asynchronous operations are commonplace in Flutter applications, especially when dealing with network requests, file operations, or animations. Dart, the programming language used in Flutter, provides powerful asynchronous programming features like async/await and Futures. By utilizing these constructs, you can handle asynchronous operations more efficiently and avoid potential side effects. The async/await syntax simplifies writing asynchronous code by allowing you to write asynchronous operations in a more synchronous style, improving code readability and maintainability.

**Limit the Use of Global Variables:**

Global variables can introduce side effects since they can be accessed and modified from anywhere within your application. It is advisable to minimise their usage and instead encapsulate related data and functionality within specific components. By localising the scope of variables, you reduce the chances of unintended side effects and make your code more modular and testable.

**Implement Thorough Testing:**

Testing is a critical aspect of any software development process, and Flutter is no exception. Comprehensive unit and integration testing can help identify and prevent side effects in your application. Writing tests that cover various scenarios and edge cases enables you to verify the behaviour of different components and ensure that side effects are handled correctly. Automated tests act as a safety net, allowing you to catch regressions when making changes and providing confidence in the stability of your codebase.


Avoiding side effects is crucial for creating reliable and maintainable Flutter applications. By adopting a reactive programming approach, utilizing appropriate state management libraries, leveraging async/await and Futures, limiting global variables, implementing thorough testing, employing design patterns and architectural principles, and leveraging Flutter's built-in widgets and APIs, you can significantly reduce the occurrence of side effects in your codebase. Prioritising the avoidance of side effects will lead to more predictable, performant, and bug-free Flutter applications, ensuring a delightful user experience and long-term success.