Declarations

Varjus supports variable declarations using let and const. Unlike some other languages, it does not support chaining declarations with the comma operator.

Using let

let declares a mutable variable, meaning its value can be reassigned.

let x = 10;
x = 20; // Allowed
console.log(x); // 20

Using const

const declares an immutable variable, meaning its value cannot be reassigned after initialization.

const y = 30;
y = 40; // Error: Cannot reassign a constant variable

const and Objects

While const prevents reassignment of the variable itself, it does not make objects immutable. You can modify the properties of a const object.

const obj = { key: "value" };
obj.key = "new value"; // Allowed
console.log(obj.key); // "new value"

obj = {}; // Error: Cannot reassign a constant variable

const and Arrays

Similarly, arrays declared with const cannot be reassigned, but their elements can be modified.

const arr = [1, 2, 3];
arr[0] = 10; // Allowed
console.log(arr); // [10, 2, 3]

arr = [4, 5, 6]; // Error: Cannot reassign a constant variable

Scope

Both let and const are block-scoped, meaning they only exist within the block {} in which they are declared.

{
    let a = 5;
    console.log(a); // 5
}
console.log(a); // Error: a is not defined