Naming Conventions: Choosing good variable names makes your code more readable and understandable.

• Start with a letter, underscore (_), or dollar sign ($): Variable names cannot start with a number.
• Subsequent characters: Can be letters, numbers, underscores, or dollar signs.
• Case-sensitive: myVariable is different from MyVariable.
• CamelCase: Commonly used in JavaScript (e.g., firstName, totalAmount). The first word is lowercase, and subsequent words start with an uppercase letter.
• Avoid reserved keywords: You cannot use JavaScript keywords (like let, const, if, for, function) as variable names.
• Descriptive names: Choose names that clearly indicate the variable's purpose (e.g., userName instead of u or x).

Reassignment:

• Variables declared with let can be reassigned to a new value.

  let score = 100;
  score = 150; // Valid
  

• Variables declared with const cannot be reassigned.

  const apiKey = "xyz123";
  // apiKey = "abc789"; // This would cause an error
  

  Note: If a const variable holds an object or an array, the object/array itself is still mutable (its properties or elements can be changed), but the variable cannot be reassigned to a new object/array.

Shadowing: Variable shadowing occurs when a variable declared within a certain scope (e.g., inside a function or a block) has the same name as a variable declared in an outer scope. The inner variable "shadows" or hides the outer variable within its scope.

let x = 10; // Outer scope x

function example() {
  let x = 20; // Inner scope x, shadows the outer x
  console.log(x); // Prints 20
}

example();
console.log(x); // Prints 10 (outer scope x is unaffected)

While shadowing is allowed, it can sometimes make code harder to understand and debug if not used carefully.