TypeScript in React: Best Practices

interface ButtonProps {
  text: string;
  onClick: () => void;
  variant?: "primary" | "secondary";
  disabled?: boolean;
}

const Button: React.FC<ButtonProps> = ({
  text,
  onClick,
  variant = "primary",
  disabled = false,
}) => {
  return (
    <button
      className={`btn btn-${variant}`}
      onClick={onClick}
      disabled={disabled}
    >
      {text}
    </button>
  );
};

import React, { useState } from "react";

interface User {
  id: number;
  name: string;
  email: string;
}

const UserProfile: React.FC = () => {
  const [user, setUser] = useState<User | null>(null);
  const [loading, setLoading] = useState<boolean>(false);

  const fetchUser = async (id: number) => {
    setLoading(true);
    try {
      const response = await fetch(`/api/users/${id}`);
      const userData: User = await response.json();
      setUser(userData);
    } catch (error) {
      console.error("Error fetching user:", error);
    } finally {
      setLoading(false);
    }
  };

  return (
    <div>
      {loading ? (
        <p>Loading...</p>
      ) : user ? (
        <div>
          <h1>{user.name}</h1>
          <p>{user.email}</p>
        </div>
      ) : (
        <p>No user data</p>
      )}
    </div>
  );
};

import React, { useReducer } from "react";

interface TodoState {
  todos: Todo[];
  filter: "all" | "completed" | "active";
}

interface Todo {
  id: number;
  text: string;
  completed: boolean;
}

type TodoAction =
  | { type: "ADD_TODO"; payload: string }
  | { type: "TOGGLE_TODO"; payload: number }
  | { type: "SET_FILTER"; payload: TodoState["filter"] };

const todoReducer = (state: TodoState, action: TodoAction): TodoState => {
  switch (action.type) {
    case "ADD_TODO":
      return {
        ...state,
        todos: [
          ...state.todos,
          { id: Date.now(), text: action.payload, completed: false },
        ],
      };
    case "TOGGLE_TODO":
      return {
        ...state,
        todos: state.todos.map((todo) =>
          todo.id === action.payload
            ? { ...todo, completed: !todo.completed }
            : todo,
        ),
      };
    case "SET_FILTER":
      return {
        ...state,
        filter: action.payload,
      };
    default:
      return state;
  }
};

import React, { ChangeEvent, FormEvent } from "react";

const ContactForm: React.FC = () => {
  const [formData, setFormData] = useState({
    name: "",
    email: "",
    message: "",
  });

  const handleInputChange = (
    e: ChangeEvent<HTMLInputElement | HTMLTextAreaElement>,
  ) => {
    const { name, value } = e.target;
    setFormData((prev) => ({
      ...prev,
      [name]: value,
    }));
  };

  const handleSubmit = (e: FormEvent<HTMLFormElement>) => {
    e.preventDefault();
    console.log("Form submitted:", formData);
  };

  return (
    <form onSubmit={handleSubmit}>
      <input
        type="text"
        name="name"
        value={formData.name}
        onChange={handleInputChange}
        placeholder="Your name"
      />
      <input
        type="email"
        name="email"
        value={formData.email}
        onChange={handleInputChange}
        placeholder="Your email"
      />
      <textarea
        name="message"
        value={formData.message}
        onChange={handleInputChange}
        placeholder="Your message"
      />
      <button type="submit">Send</button>
    </form>
  );
};

interface ListProps<T> {
  items: T[];
  renderItem: (item: T) => React.ReactNode;
  keyExtractor: (item: T) => string | number;
}

function List<T>({ items, renderItem, keyExtractor }: ListProps<T>) {
  return (
    <ul>
      {items.map((item) => (
        <li key={keyExtractor(item)}>{renderItem(item)}</li>
      ))}
    </ul>
  );
}

// Usage
const users: User[] = [
  { id: 1, name: "John", email: "john@example.com" },
  { id: 2, name: "Jane", email: "jane@example.com" },
];

<List
  items={users}
  renderItem={(user) => (
    <span>
      {user.name} ({user.email})
    </span>
  )}
  keyExtractor={(user) => user.id}
/>;

import { useState, useEffect } from "react";

interface FetchState<T> {
  data: T | null;
  loading: boolean;
  error: string | null;
}

function useFetch<T>(url: string): FetchState<T> {
  const [state, setState] = useState<FetchState<T>>({
    data: null,
    loading: true,
    error: null,
  });

  useEffect(() => {
    const fetchData = async () => {
      try {
        setState((prev) => ({ ...prev, loading: true }));
        const response = await fetch(url);
        if (!response.ok) {
          throw new Error(`HTTP error! status: ${response.status}`);
        }
        const data: T = await response.json();
        setState({ data, loading: false, error: null });
      } catch (error) {
        setState({
          data: null,
          loading: false,
          error: error instanceof Error ? error.message : "An error occurred",
        });
      }
    };

    fetchData();
  }, [url]);

  return state;
}

// tsconfig.json
{
  "compilerOptions": {
    "strict": true,
    "noImplicitAny": true,
    "noImplicitReturns": true,
    "noUnusedLocals": true,
    "noUnusedParameters": true
  }
}

// Good for unions
type Status = "loading" | "success" | "error";

// Good for object shapes
interface User {
  id: number;
  name: string;
  email: string;
}

// Partial for optional properties
const updateUser = (id: number, updates: Partial<User>) => {
  // Implementation
};

// Pick for selecting specific properties
type UserPreview = Pick<User, "id" | "name">;

// Omit for excluding properties
type CreateUserRequest = Omit<User, "id">;