Function scope

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

Function scope

When you declare a variable inside a function, it becomes local and lives only inside that function. When the function ends, the local variable disappears.

This lets each function keep its own private space. In function add(a, b) { let sum = a + b; return sum; }, sum can only be read inside add; reaching it from outside throws an error.

Local variables and the scope principle

The reason local variables cannot be reached from outside is the scope principle: each scope creates its own variables, and outer scopes cannot see the variables of inner scopes. Access goes from outside in; it is closed from inside out.

So a function can read a total declared outside it, but code outside cannot read a total declared inside the function. This prevents you from accidentally changing another function's variable and keeps the code safer.

Exercise Compute with a local variable

Define a function called multiply(a, b). Inside it, create a local variable named result holding the value a * b, and return result. Then assign the result of multiply(6, 7) to a variable answer and log it with console.log(answer).

Show example solution

function multiply(a, b) {
  let result = a * b;
  return result;
}

const answer = multiply(6, 7);
console.log(answer);

Test yourself

What does this code output?
```
function make() {
  let item = 'pencil';
  return item;
}
console.log(item);
```
- pencil
- undefined
- ReferenceError
- null
Show answer

ReferenceError — Correct. item is local to the function, so it cannot be reached from outside.

Complete the local variable

function add(a, b) {
  let sum = a + b;
  return ____;
}

Show answer

function add(a, b) {
  let sum = a + b;
  return sum;
}

Match the access

Inner to outer variable

Accessible
Outer to inner variable

Not accessible
Two vars in same scope

See each other
Local after function ends

Goes away

Next lesson: Block scope

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