This type of variable is defined inside a function and is not accessible outside the function.

Global Variables

In Python, a variable declared outside of the function or in global scope is known as a global variable. This means that a global variable can be accessed inside or outside of the function.

Let's see an example of how a global variable is created in Python.

Example 1: Create a Global Variable

x = "global"

def foo():
    print("x inside:", x)


foo()
print("x outside:", x)

Output

x inside: global
x outside: global

In the above code, we created x as a global variable and defined a foo() to print the global variable x. Finally, we call the foo() which will print the value of x.

What if you want to change the value of x inside a function?

x = "global"

def foo():
    x = x * 2
    print(x)

foo()

Output

UnboundLocalError: local variable 'x' referenced before assignment

The output shows an error because Python treats x as a local variable and x is also not defined inside foo().

To make this work, we use the global keyword. Visit Python Global Keyword to learn more.

Local Variables

A variable declared inside the function's body or in the local scope is known as a local variable.

Example 2: Accessing local variable outside the scope

def foo():
    y = "local"


foo()
print(y)

Output

NameError: name 'y' is not defined

The output shows an error because we are trying to access a local variable y in a global scope whereas the local variable only works inside foo() or local scope.

Let's see an example on how a local variable is created in Python.

Example 3: Create a Local Variable

Normally, we declare a variable inside the function to create a local variable.

def foo():
    y = "local"
    print(y)

foo()

Output

local

Let's take a look at the earlier problem where x was a global variable and we wanted to modify x inside foo().

Global and local variables

Here, we will show how to use global variables and local variables in the same code.

Example 4: Using Global and Local variables in the same code

x = "global "

def foo():
    global x
    y = "local"
    x = x * 2
    print(x)
    print(y)

foo()

Output

global global 
local

In the above code, we declare x as a global and y as a local variable in the foo(). Then, we use multiplication operator * to modify the global variable x and we print both x and y.

After calling the foo(), the value of x becomes global global because we used the x * 2 to print two times global. After that, we print the value of local variable y i.e local.

Example 5: Global variable and Local variable with same name

x = 5

def foo():
    x = 10
    print("local x:", x)


foo()
print("global x:", x)

Output

local x: 10
global x: 5

In the above code, we used the same name x for both global variable and local variable. We get a different result when we print the same variable because the variable is declared in both scopes, i.e. the local scope inside foo() and global scope outside foo().

When we print the variable inside foo() it outputs local x: 10. This is called the local scope of the variable.

Similarly, when we print the variable outside the foo(), it outputs global x: 5. This is called the global scope of the variable.

Nonlocal Variables

Nonlocal variables are used in nested functions whose local scope is not defined. This means that the variable can be neither in the local nor the global scope.

Let's see an example of how a nonlocal variable is used in Python.

We use nonlocal keywords to create nonlocal variables.

Example 6: Create a nonlocal variable

def outer():
    x = "local"

    def inner():
        nonlocal x
        x = "nonlocal"
        print("inner:", x)

    inner()
    print("outer:", x)


outer()

Output

inner: nonlocal
outer: nonlocal

In the above code, there is a nested inner() function. We use nonlocal keywords to create a nonlocal variable. The inner() function is defined in the scope of another function outer().

Note : If we change the value of a nonlocal variable, the changes appear in the local variable.

Scope determines the accessibility (visibility) of variables.

JavaScript has 3 types of scope:

• Block scope
• Function scope
• Global scope

Block Scope

Before ES6 (2015), JavaScript had only Global Scope and Function Scope.

ES6 introduced two important new JavaScript keywords: let and const.

These two keywords provide Block Scope in JavaScript.

Variables declared inside a { } block cannot be accessed from outside the block:

Example

{
  let x = 2;
}
// x can NOT be used here

Variables declared with the var keyword can NOT have block scope.

Variables declared inside a { } block can be accessed from outside the block.

Example

{
  var x = 2;
}
// x CAN be used here

Local Scope

Variables declared within a JavaScript function, become LOCAL to the function.

Example

// code here can NOT use carName

function myFunction() {
  let carName = "Volvo";
  // code here CAN use carName
}

// code here can NOT use carName

Try it Yourself »

Local variables have Function Scope:

They can only be accessed from within the function.

Since local variables are only recognized inside their functions, variables with the same name can be used in different functions.

Local variables are created when a function starts, and deleted when the function is completed.

Function Scope

JavaScript has function scope: Each function creates a new scope.

Variables defined inside a function are not accessible (visible) from outside the function.

Variables declared with var, let and const are quite similar when declared inside a function.

They all have Function Scope:

function myFunction() {
  var carName = "Volvo";   // Function Scope
}

function myFunction() {
  let carName = "Volvo";   // Function Scope
}

function myFunction() {
  const carName = "Volvo";   // Function Scope
}

Global JavaScript Variables

A variable declared outside a function, becomes GLOBAL.

Example

let carName = "Volvo";
// code here can use carName

function myFunction() {
// code here can also use carName
}

Try it Yourself »

A global variable has Global Scope:

All scripts and functions on a web page can access it. 

Global Scope

Variables declared Globally (outside any function) have Global Scope.

Global variables can be accessed from anywhere in a JavaScript program.

Variables declared with var, let and const are quite similar when declared outside a block.

They all have Global Scope:

var x = 2;       // Global scope

let x = 2;       // Global scope

const x = 2;       // Global scope

JavaScript Variables

In JavaScript, objects and functions are also variables.

Scope determines the accessibility of variables, objects, and functions from different parts of the code.

Automatically Global

If you assign a value to a variable that has not been declared, it will automatically become a GLOBAL variable.

This code example will declare a global variable carName, even if the value is assigned inside a function.

Example

myFunction();

// code here can use carName

function myFunction() {
  carName = "Volvo";
}

Try it Yourself »

Strict Mode

All modern browsers support running JavaScript in "Strict Mode".

You will learn more about how to use strict mode in a later chapter of this tutorial.

In "Strict Mode", undeclared variables are not automatically global.

Global Variables in HTML

With JavaScript, the global scope is the JavaScript environment.

In HTML, the global scope is the window object.

Global variables defined with the var keyword belong to the window object:

Global variables defined with the let keyword do not belong to the window object:

Example

let carName = "Volvo";
// code here can not use window.carName

Try it Yourself »

Warning

Do NOT create global variables unless you intend to.

Your global variables (or functions) can overwrite window variables (or functions).
Any function, including the window object, can overwrite your global variables and functions.

The Lifetime of JavaScript Variables

The lifetime of a JavaScript variable starts when it is declared.

Function (local) variables are deleted when the function is completed.

In a web browser, global variables are deleted when you close the browser window (or tab).

Function Arguments

Function arguments (parameters) work as local variables inside functions.

What variable is defined inside a function and is not accessible outside the function?

What type of variables are defined outside of a function?

Which variable can be used inside and outside the function?

What is the variable called when it is defined inside a function?