Don't Use Effects To Derive Values And Learn How Svelte Works

Understanding Signals and Reactivity in SW 5

SW 5 introduces a new reactivity system called runes.
The reactivity system allows you to declare state using the syntax "$State" and pass values using "$derived".
Signals become reactive when written to and can be read using "derive".
Signals are objects with subscribers and other properties.
Derives are functions that get turned into signals and can take simple expressions.
Signals are read within effects and added to subscribers.
Setting a value for a signal triggers the update and notifies subscribers.
Signals provide a simple and effective way to create reactivity in SW 5.

SWEL uses proxies under the hood to enable reactive behavior.
Proxies allow for direct manipulation of objects and arrays, such as using push to add items to an array.
Exporting from a SWEL file creates global state, thanks to the use of proxies.
SWEL provides the derived function for more complex computations.
Side effects, such as modifying external variables, should be avoided in SWEL to prevent unexpected behavior.
The SWEL compiler can provide warnings for unsafe mutations within derived functions.
It is possible to bypass warnings by returning a function from within a derived function, but this can lead to potential issues.

Avoid writing to external state or values in derived functions.
Use derived functions to derive values rather than writing to them.
If you need to write to external state, use a regular effect outside of the derived function.
Use the `effect` function to write to external state, passing in the value that triggers the effect.
Avoid using effects or complex logic inside derived functions.
Be aware of potential infinite loops when using derived functions with reactive values.
Consider using the `untrack` function to prevent reactivity in certain cases.
Avoid using closure to maintain state inside derived functions.

Writing values in effects can lead to convoluted code and potential problems.
It is recommended to read values instead of writing to them when using effects.
Effects should be used for side effects, not for modifying state or values.
Using derives can help avoid the need for writing values in effects.
Writing values in effects can lead to synchronization issues, as effects run last in the event loop.
Effects should be used sparingly and only for specific purposes.

Derived values offer advantages in terms of caching and efficiency.
Derived values can be used instead of regular functions to compute values.
Using derived values can reduce the need for repetitive computation.
Derived values are particularly useful in complex scenarios, such as managing a shopping cart.
There is no significant performance penalty associated with using derived values.
However, it is also possible to achieve similar results by using regular functions, although the developer experience may be less convenient.

Derived signals allow for efficient updating of values without unnecessary computation.
Using derived signals can help optimize performance by only updating values when necessary.
Derived signals can be easily implemented in JavaScript using simple code structures.
Derived signals can be used to track changes in arrays or other data structures without manually checking for updates.
Derived signals provide a concise and efficient way to keep track of values and update them when needed.

Derivs are similar to effects, where a function is passed to them.
To use derivs, create a signal source and pass the function to set signal.
Derivs rerun the function each time it updates its subscribers.
Derivs cannot be used to bind values as they are read-only.
Regular functions can be used to synchronize state instead of derivs.
An example is shown where two values are synchronized using regular functions.
Another option is to create a variable derived using getters and setters.
An example using getters and setters is shown to synchronize state.
The choice between regular functions and derived variables depends on preference.

Using a function or class to neatly bind and manipulate values without user input.
Utilizing getter and setter methods to synchronize Celsius and Fahrenheit temperature values.
Creating a private value for the object and using getter and setter functions to update values.
Applying formulas to convert Celsius to Fahrenheit and vice versa.
Demonstrating the use of State in a class to simplify value binding and manipulation.

Returning a value that assigns some State can cause trouble when trying to derive something from it.
Value derivations are lazy and only update when their value updates, which can cause issues when the same value is returned multiple times in a row.
Using value derivations in this way is not like a dependency array that always reruns when the value updates.
Signals are a better alternative to value derivations because they only rerun when the value updates, making them more efficient.
If faced with a situation like this, it's better to update everything inside the relevant function rather than relying on value derivations.
When using classes, the "this" keyword may cause issues, but arrow functions or binding can help resolve them.
You don't have to use classes and can use functions or other approaches instead.
Consider whether or not you actually need to use value derivations, as simpler alternatives may be available.
Value derivations can be useful for calculating percentages or other more complex operations, but simple calculations can be done without them.

Getters and setters can be defined by the user.
It is a simple process.
By defining getters and setters, you have more control over the access and manipulation of class attributes.