Add in Notes Reacts

In Vite , you have to make .jsx file explicityly, .js not considered as .jsx

In JavaScript, backticks (`) are used for template literals, which allow you to embed expressions and variables inside strings easily.

Advantages of Backticks (Template Literals):

1. String Interpolation (Embedding Variables/Expressions): Backticks allow you to insert variables or expressions directly into a string without needing string concatenation.

   const hostname = '127.0.0.1';
   const port = 3000;
   console.log(`Server running at http://${hostname}:${port}/`);

   In the example above:

   • ${hostname} is replaced with the value of the hostname variable.
   • ${port} is replaced with the value of the port variable.

2. Multi-line Strings: Backticks allow strings to span multiple lines without the need for escape characters (like \n for newlines).

   const multilineString = `
     This is
     a multi-line
     string.`;
   console.log(multilineString);

3. Expressions in Templates: You can directly embed any JavaScript expression inside ${} inside a template literal.

   const sum = 5 + 3;
   console.log(`The sum of 5 and 3 is ${sum}`); // "The sum of 5 and 3 is 8"

Why Backticks in console.log() Example?

In your example:

console.log(`Server running at http://${hostname}:${port}/`);

• Backticks are used to insert the values of hostname and port into the string.
• It's more readable and easier than using concatenation (e.g., 'Server running at http://' + hostname + ':' + port + '/').

Using backticks makes the code cleaner and more maintainable.

setCount([newCount, ...counts]) is commonly used in React when working with a state array to add a new value to the beginning of the array while preserving the existing values. Let’s break it down:

Explanation

1. newCount:

   • The new value you want to add to the state array.

2. ...counts:

   • The spread operator is used to unpack the current values of the counts array.

3. [newCount, ...counts]:

   • Creates a new array where newCount is added at the beginning, followed by all the elements from the existing counts array.

4. setCount:

   • Updates the state with the new array.

Example

Suppose you’re managing an array of counts in a React component:

import React, { useState } from 'react';
 
function App() {
  const [counts, setCounts] = useState([10, 20, 30]);
 
  const addNewCount = () => {
    const newCount = 5;
    setCounts([newCount, ...counts]); // Adds newCount at the beginning
  };
 
  return (
    <div>
      <button onClick={addNewCount}>Add Count</button>
      <ul>
        {counts.map((count, index) => (
          <li key={index}>{count}</li>
        ))}
      </ul>
    </div>
  );
}
 
export default App;

How It Works

1. Initial state: [10, 20, 30].
2. When the button is clicked:
   • newCount = 5.
   • setCounts([newCount, ...counts]) creates a new array [5, 10, 20, 30].
   • React updates the counts state to this new array.
3. The UI re-renders to display the updated state.

Key Points

• Immutability: Using [newCount, ...counts] ensures immutability by creating a new array instead of modifying the original counts array.
• Order: Adding newCount at the beginning ([newCount, ...counts]) ensures the new value appears first. To add it at the end, use [...counts, newCount].
• Efficiency: Although this approach is straightforward, be mindful of performance if the array grows very large, as spreading arrays can become costly.

Adding at the End

If you want to add newCount at the end of the array:

setCounts([...counts, newCount]);