JavaScript Scope – Global and Local Variables

Scope in JavaScript defines where a variable is accessible or "visible" in your code. Understanding scope is essential for writing predictable and bug-free JavaScript programs.

What is Scope?

In JavaScript, scope refers to the context in which variables are declared and accessible. There are two main types:

• Global Scope
• Local Scope

Modern JavaScript also introduces block scope with let and const.

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1. Global Scope

A variable declared outside any function or block is in the global scope and can be accessed anywhere in the code.

Example: Global Variable

Global variables are accessible throughout your code. Avoid overusing them to prevent conflicts and bugs.

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2. Local Scope

A variable declared inside a function is a local variable. It is only accessible within that function.

Example: Local Variable

Local variables help avoid conflicts and keep code modular.

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3. Block Scope with let and const

Variables declared with let or const inside curly braces {} (like in if, for, or while) are only available inside that block.

Example: Block Scope

var does not have block scope — it is hoisted to the function level. Use let and const to ensure predictable, block-level scoping.

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Key Takeaways

• Global variables are declared outside all functions and accessible everywhere.
• Local variables are declared inside functions and cannot be accessed outside.
• Use let and const for block-level scoping.
• Avoid unnecessary global variables to prevent name collisions.
• Understanding scope helps write cleaner, modular, and safer JavaScript code.