feat: add javascript/typescript guidelines to gemini.md (#375)

GEMINI.md

@@ -22,6 +22,35 @@ When writing tests look at existing tests in packages/server and packages/cli to
 
 The main branch for this project is called "main"
 
+## JavaScript/TypeScript
+
+When contributing to this React, Node, and TypeScript codebase, please prioritize the use of plain JavaScript objects with accompanying TypeScript interface or type declarations over JavaScript class syntax. This approach offers significant advantages, especially concerning interoperability with React and overall code maintainability.
+
+### Preferring Plain Objects over Classes
+
+JavaScript classes, by their nature, are designed to encapsulate internal state and behavior. While this can be useful in some object-oriented paradigms, it often introduces unnecessary complexity and friction when working with React's component-based architecture. Here's why plain objects are preferred:
+
+- Seamless React Integration: React components thrive on explicit props and state management. Classes' tendency to store internal state directly within instances can make prop and state propagation harder to reason about and maintain. Plain objects, on the other hand, are inherently immutable (when used thoughtfully) and can be easily passed as props, simplifying data flow and reducing unexpected side effects.
+
+- Reduced Boilerplate and Increased Conciseness: Classes often promote the use of constructors, this binding, getters, setters, and other boilerplate that can unnecessarily bloat code. TypeScript interface and type declarations provide powerful static type checking without the runtime overhead or verbosity of class definitions. This allows for more succinct and readable code, aligning with JavaScript's strengths in functional programming.
+
+- Enhanced Readability and Predictability: Plain objects, especially when their structure is clearly defined by TypeScript interfaces, are often easier to read and understand. Their properties are directly accessible, and there's no hidden internal state or complex inheritance chains to navigate. This predictability leads to fewer bugs and a more maintainable codebase.
+  Simplified Immutability: While not strictly enforced, plain objects encourage an immutable approach to data. When you need to modify an object, you typically create a new one with the desired changes, rather than mutating the original. This pattern aligns perfectly with React's reconciliation process and helps prevent subtle bugs related to shared mutable state.
+
+- Better Serialization and Deserialization: Plain JavaScript objects are naturally easy to serialize to JSON and deserialize back, which is a common requirement in web development (e.g., for API communication or local storage). Classes, with their methods and prototypes, can complicate this process.
+
+### Embracing JavaScript's Array Operators
+
+To further enhance code cleanliness and promote safe functional programming practices, leverage JavaScript's rich set of array operators as much as possible. Methods like `.map()`, `.filter()`, `.reduce()`, `.slice()`, `.sort()`, and others are incredibly powerful for transforming and manipulating data collections in an immutable and declarative way.
+
+Using these operators:
+
+- Promotes Immutability: Most array operators return new arrays, leaving the original array untouched. This functional approach helps prevent unintended side effects and makes your code more predictable.
+- Improves Readability: Chaining array operators often leads to more concise and expressive code than traditional for loops or imperative logic. The intent of the operation is clear at a glance.
+- Facilitates Functional Programming: These operators are cornerstones of functional programming, encouraging the creation of pure functions that take inputs and produce outputs without causing side effects. This paradigm is highly beneficial for writing robust and testable code that pairs well with React.
+
+By consistently applying these principles, we can maintain a codebase that is not only efficient and performant but also a joy to work with, both now and in the future.
+
 ## React (prompt copied the experimental react-mcp-server)
 
 ### Role