Understanding the basics

JavaScript provides two important keywords for variable declaration: let and const. In this blog post, we will explore the differences between them and when to use each one.

let Keyword

The let keyword allows you to declare variables that are limited in scope to the block, statement, or expression in which they are used. This is unlike the var keyword, which defines a variable globally or locally to an entire function regardless of block scope.

let x = 10;
if (x === 10) {
  let y = 20;
  console.log(y); // 20
}
console.log(y); // ReferenceError: y is not defined

In the above example, y is only accessible within the if block.

const Keyword

The const keyword is used to declare variables that are read-only. This means that once a value is assigned to a const variable, it cannot be reassigned. However, it does not mean the value itself is immutable.

const z = 30;
z = 40; // TypeError: Assignment to constant variable.

In the above example, trying to reassign z will result in a TypeError.

Highlighting differences

• let allows reassigning the variable, while const does not.
• Both let and const are block-scoped, unlike var.
• const variables must be initialized when declared.

let a = 10;
a = 20; // OK
 
const b = 30;
b = 40; // TypeError: Assignment to constant variable.

When to use let and const

Use let when you need to reassign a variable, and use const when you want to ensure the variable cannot be reassigned.

let count = 0; // Use let when the value can change
const pi = 3.14159; // Use const for constants

Conclusion

Understanding the differences between let and const is crucial for writing clean and maintainable JavaScript code. Use let when you need to reassign a variable, and use const when you want to ensure the variable cannot be reassigned.

Happy coding!