Scope basics

Learn why variables declared inside a function are not accessible from outside.

Function scope

Variables declared with let or const inside a function only live inside that function. This is called function scope. They cannot be reached from outside.

For example: function calc() { let total = 10; return total; }. Here total lives only inside calc. If you write total outside the function, you get an error. This prevents name clashes and keeps code safe.

Local and outer variables

If a variable is declared outside a function, the function can still reach it. This is the outer scope. But if you declare a variable with the same name inside the function, the inner one hides the outer; this is called shadowing.

Example: let name = "Alex"; function greet() { let name = "Sam"; console.log(name); }. Calling greet() prints Sam because the inner name shadows the outer one. The outer name stays unchanged.

Exercise Use a local variable

Define a function called makeGreeting. Inside it, declare a local variable with let message and assign it a welcome text. Then return message. Finally print the result with console.log(makeGreeting()).

Show example solution

function makeGreeting() {
  let message = "Welcome";
  return message;
}

console.log(makeGreeting());

Test yourself

Can you reach total from outside the function?
```
function calc() {
  let total = 10;
  return total;
}
console.log(total);
```
- Yes, it prints 10
- No, it throws ReferenceError
- Yes, it prints undefined
- No, it is silently skipped
Show answer

No, it throws ReferenceError — Correct. total is in function scope, not reachable from outside.

Declare a local variable

function showName() {
  ____ name = "Alex";
  console.log(name);
}
showName();

Show answer

function showName() {
  let name = "Alex";
  console.log(name);
}
showName();

Match each variable to its scope

let inside a function

Local scope
let outside a function

Outer scope
inner hides outer

Shadowing
access inner from outside

ReferenceError

Next lesson: Summary - Functions

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