Global scope

Learn that variables declared in global scope are accessible everywhere.

What is global scope?

Global scope is the area where variables written at the outermost level live. When you declare a variable outside any function or block, it becomes global and can be accessed from anywhere in the code.

For example, an appName variable declared at the top can be read both inside and outside functions. This makes global variables handy for shared state; but using too many makes the code harder to follow.

The global object (window/globalThis)

In the browser, global scope is tied to the global object. In browsers this object is window; the modern, environment-agnostic name is globalThis.

Variables declared with var at the top level become properties of window: writing var appName = 'Stock'; makes window.appName work too. let and const live in the global scope but are not added to window. Knowing this difference helps when reading old code.

Exercise Use a global variable

Declare a global variable named appName with the value "Stock". Write a function called showApp() that logs appName with console.log from inside. Then call the function.

Show example solution

let appName = "Stock";

function showApp() {
  console.log(appName);
}

showApp();

Test yourself

Which of these is a global variable?
```
let counter = 0;
function inc() { counter++; }
```
- counter declared at the top, outside any function
- counter declared inside the inc function
- counter declared inside an if block
- counter declared inside a for loop
Show answer

counter declared at the top, outside any function — Correct. counter is global because it is declared in the outer scope.

Declare the global variable

let appName = ____;

Show answer

let appName = "Stock";

Match the scope type to its example

Global scope

Declared outside any function
Function scope

Declared inside a function
Block scope

Declared with let in a block
Hoisting

Declaration is lifted up

Next lesson: Function scope

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