JS Tutorial

JavaScript const

The const keyword is used to declare **block-scoped constants**. Once a value is assigned to a const variable, it **cannot be reassigned**. It was introduced in ES6 (ECMAScript 2015) and is ideal for values that should not change.

📐 Syntax:

const pi = 3.14;
// pi = 3.14159 ❌ Error: Assignment to constant variable

🧪 Try it Live:

Click the button to test how const behaves:

📦 Features of const:

• Block Scoped: Like let, it's accessible only within the block.
• Cannot be reassigned: Once assigned, the value stays fixed.
• Cannot be re-declared: Declaring again in the same scope throws an error.

🧠 Example:

{
  const language = "JavaScript";
  console.log(language); // JavaScript
  // language = "Python"; ❌ Error
}

📁 Objects and Arrays with const:

You can't reassign the object/array, but you can change its content:

const user = { name: "Alice" };
user.name = "Bob"; // ✅ Allowed
// user = { name: "Charlie" }; ❌ Error

📝 Best Practice:

Use const by default. Only use let if you know the value will change.