React.js

1. React and State Management

State Management Hooks:

useState():
- useState is a hook that manages state in functional components.
- It returns an array containing the state variable and a setter function.
- Example:
```
  const [count, setCount] = useState(0);
```
- To update the state, call the setter function (setCount), and to use the state, refer to the state variable (count).

useEffect():

useEffect handles side effects in functional components.
It accepts a function and a list of dependencies.
The effect function runs after the component renders and re-runs when dependencies change.

Example:

     useEffect(() => {
          getCandidateInformation()
              .then((response: CandidateModel) => {
                  setCandidate(response);
                  setIsLoading(false);
              })
              .catch((err) => {
                  console.error('Error loading candidate information:', err);
                  setError('Error loading candidate information.');
                  setIsLoading(false);
              });
      }, []);

Array Transformation:

map():
- map is a method that transforms each element of an array.
- It takes a callback function and returns a new array.
- Example:
```
  const numbers = [2, 4];
  const doubled = numbers.map(num => num * 2); // [4, 8]
```

Lifting State Up:

Centralize the state in a parent component.
Pass the state down to child components as props.
Child components can call functions passed as props to update the state in the parent component.

Example:

  function Parent() {
    const [state, setState] = useState(initialState);
    return <Child state={state} setState={setState} />;
  }

Context:

React Context:
- Used for sharing state across the component tree without passing props down manually.
- Useful for global settings like themes or localization.
- Example:
```
  const ThemeContext = React.createContext('light');
```

Hooks:

useRef():
- Used to access DOM elements directly.
- Example:
```
  const inputRef = useRef(null);
```

useMemo():

Memoizes a computed value to optimize performance.

Example:

  const memoizedValue = useMemo(() => computeExpensiveValue(a, b), [a, b]);

Redux:

Redux Lifecycle:
- Components trigger actions.
- Actions have types and payloads.
- Reducers handle actions and update the state.
- The state is passed to components via props.
- Example:
```
  const action = { type: 'INCREMENT' };
```

React.js:

React is a JavaScript library for building user interfaces.
It is component-based, allowing for building reusable UI components.
Data is communicated from parent to child components using props.

useReducer():

Similar to useState but for more complex state logic.

Example:

  const [state, dispatch] = useReducer(reducer, initialState);

Component Lifecycle:

In React class components, lifecycle methods include componentDidMount, componentDidUpdate, and componentWillUnmount.

JavaScript Concepts:

Event Loop:
- JavaScript is single-threaded but can handle asynchronous operations using the event loop.
- Node.js extends JavaScript capabilities on the server side.
- Example:
```
  setTimeout(() => console.log('Hello'), 1000);
```

2. Basic Pull Requests

Pull Requests:

Ensure the code is clean and well-documented.
Write tests for new features or changes.
Respond to comments constructively and make necessary improvements.

Handling Disagreements:

Discuss and justify your approach politely.
Be open to suggestions and willing to make changes.

Defining State in Class-Based Components:

Define the state inside the constructor.

Example:

  class MyComponent extends React.Component {
    constructor(props) {
      super(props);
      this.state = { count: 0 };
    }
  }

Hooks and Optimization:

useState():
- Updating state triggers a re-render.
useMemo():
- Avoid unnecessary re-computation.
- Use it for expensive calculations.
- Use for static components.
- Example:
```
  const memoizedValue = useMemo(() => computeExpensiveValue(a, b), [a, b]);
```

Referential Equality:

Comparing arrays and objects checks references, not values.

useRef() and useContext():

useRef():
- Access DOM elements or persist values across renders.
useContext():
- Share state across components without prop drilling.

WebSocket Protocol:

Real-time data fetching.

Example:

  const socket = io('http://localhost:3000');

Context API and Redux:

Context API:
- Avoid overuse; useful for global data like themes.
Redux:
- State management tool.
- Example:
```
  const store = createStore(reducer);
```

WebSocket Protocol:

Real-time communication between client and server.

Example:

  const socket = io('http://localhost:3000');

Conclusion

Familiarity with state management, React hooks, Redux, and JavaScript fundamentals will prepare you for technical interviews and help you when building your own projects :)

Technical Frontend Interviews Topics: React.js

1. React and State Management

2. Basic Pull Requests

Conclusion