Variable Scope in JavaScript

1. Block Scope of Variables in JavaScript
2. Local Scope of Variables in JavaScript
3. Global Scope of Variables in JavaScript

The scope of a variable is the accessibility or visibility of the variable in the program.

We have three types of variable scope in JavaScript. These are the Block, Local, and Global scope.

Let us discuss these in this article.

Block Scope of Variables in JavaScript

Before the introduction of ES6 in 2015, Javascript only had the Global and Function scope. After the introduction of ES6, two new keywords were introduced, let and const. These keywords made the block scope a possibility.

Variables declared within the curly braces {} fall under the block scope as we can not access them from outside the block.

See the code below.

{ let a = 17; }
// a cannot be used here from outside the block

Variables declared using the keyword var cannot have block scope.

For example,

{ var a = 17 }
// a can be used here from outside the block

Local Scope of Variables in JavaScript

A variable in JavaScript has the local scope when it is declared within a function. These are not accessible from outside the function.

For example,

function sampleFunction() {
  let myName = 'Hemank';
}
// myName cannot be accessed here

Variables declared with the var, let, and const keywords all have function scope.

Global Scope of Variables in JavaScript

All the variables that are defined outside a function are global. These are accessible anywhere in the program and not limited to any function.

For example,

let myName = 'Ella'
// we can access the above variable here

function sampleFunc() {
  // myName can be access from within a function as well.
}

In the above code, the declaration of the variable myName was outside the function. Thus, it has become global and can be used from within the function or outside the function.