Scope

Scope decides where a variable "lives" and where you are allowed to reference it. A variable declared inside a function is not visible outside that function — its scope is local. A variable declared at the top level of the file is global and visible everywhere.

Scope prevents naming collisions. You can have a variable called i inside one function and another i inside a different function, and they will not interfere with each other because each has its own local scope.

Most modern languages use lexical (static) scope — the scope is determined by where the variable is written in the source code, not by where the function is called. Block scope (introduced by let and const in JavaScript) confines a variable to the nearest curly-brace block.

1. Global scope — variables declared outside any function or block; visible everywhere.
2. Function scope — variables declared inside a function; visible only within that function.
3. Block scope — variables declared with let/const inside {}; visible only in that block.
4. When code references a variable, the interpreter searches the current scope, then outer scopes, up to global.