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JavaScript Scope

Scope is where a name can be seen. A name declared in one place may stay hidden from other places.

A local name

Scope is where a name can be seen, and this name lives inside one function. The function reads and logs its own local name.

function showName() {
  const name = "Ana";
  console.log(name);
}
showName();

A global name

city sits at the top level of this script. The function reads the global name and logs it.

const city = "Oslo";
function showCity() {
  console.log(city);
}
showCity();
console.log(city);

Separate locals

Each function declares its own label here. The two locals hold different values and never mix.

function first() {
  const label = "First";
  console.log(label);
}
function second() {
  const label = "Second";
  console.log(label);
}
first();
second();

Example

let score = 10;
{
  let score = 99;
  console.log(score);
}
console.log(score);
function showScore() {
  const score = 42;
  console.log(score);
}
showScore();
console.log(score);

Key points

  • Local scope: the inside of a function, where its own names live
  • Global scope: the top level of a script, seen by all code in it
  • Reading a local name from outside its function raises a ReferenceError.
  • Block scope: the inside of a pair of braces, where a let name stays
  • Hoisting: declarations rise to the top of their scope before code runs.
  • Two functions can hold separate local names that share one spelling.

In this example, the global score starts at 10. A bare block declares its own score at 99 and logs 99 inside the braces. The next line logs the global score, still 10. The showScore function holds a local score at 42 and logs it, and the last line logs the global 10 again.

Try it Yourself

Edit the code, then press Run.

Runs in your browser — the preview under the editor is the real result. Nothing is sent to a server. The code runner panel (right) does the same with more room.

Exercise

Where can a local name inside a function be read?