JavaScript const Keyword

The const keyword in JavaScript is used to declare variables that cannot be reassigned after their initial value is set. It was introduced in ES6 (ECMAScript 2015) and is ideal for values that remain constant throughout your program.

Syntax

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Example: Declaring with const

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Key Features of const

1. Block Scope

Like let, const is block-scoped and only accessible within the block it is defined in.

2. Cannot Be Reassigned

Once a value is assigned to a const variable, it cannot be changed.

3. Constant ≠ Immutable

You can modify the contents of objects or arrays declared with const, but not reassign them.

4. Must Be Initialized

const declarations must include an initial value.

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Best Practices

• Use const by default
• Use let only when reassignment is needed
• Prefer const to avoid unintended variable updates
• Use with objects and arrays whose reference shouldn't change

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Key Takeaways

• const creates read-only variables
• Reassignment is not allowed, but object mutation is
• It provides block-level scoping
• Must be initialized at the time of declaration
• Promotes safer, more predictable code
• Recommended for constants and fixed references