Scope in JavaScript

What is Scope in JavaScript? How to handle Scope in javaScript?

The scope is related to variables in the JavaScript, scope determines the accessibility or visibility of variables in the Javascript.
Before ES6, JavaScript had only two kind of scopes:

1. Global Scope
2. Function Scope

In the ES6, the Block level scope introduced with let and const keywords.

Now JavaScript has 3 types of scope:
1. Global Scope
2. Function Scope
3. Block level

Global Scope:

In the JavaScript, those variables which are declared Globally or outside the function have the global dcope in nature. Those global variables can be accessed from anywhere in that codes/program.
Examples:

                                var x = 2;       // Global scope
                                let y = 20;       // Global scope
                                const z = 21;       // Global scope
                            

In JavaScript, objects and functions are also variables.

If you write codes where you haven't declared a variable but you assigned some value to it, this also will be a global variable and scope will be global.

                                someFunction();
                                            
                                function someFunction() {
                                  name = "idkblogs";
                                }
                            

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

Function Scope:

In the javaScript, all function creates their own scope called function scope. Variables defined within the function are not accessible outside the function.
Examples:

                            function myFunction() {
                                var name = "idkblogs";   // Function Scope
                            }
                            

                            function myFunction() {
                                let name = "idkblogs";   // Function Scope
                            }
                            

                            function myFunction() {
                                const name = "idkblogs";   // Function Scope
                            }
                            

Block Scope:

When we write our code inside the {...}, the variables inside the block have Block level scope. Variables declared inside a { } block cannot be accessed from outside the block.

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

The blocl scope is not ruled on var keyword. It means aariables declared with the var keyword can NOT have block scope and variables declared inside a { } block is accessible from outside the block.

                        {
                        var num = 2;
                        }
                        // num can be used here
                        

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

Local Scope:

We have a local scope also, those variables who is declared inside the functions, has the local scope in nature.

                                // code here can NOT use myName
                    
                                function myFunction() {
                                  let myName = "idkblogs";
                                  // code here CAN use myName
                                }
                                
                                // code here can NOT use myName
                        

Local variables have their identity inside that function only where they have declared, so it provides the advantages, variables with the same name can be used in different functions. In the JavaScript, Local variables are created when a function starts, and deleted when the function is completed.

Conclusion:

In this article, we learned about the Scope in JavaScript, What is Scope in JavaScript? kind of scopes, types of scope, How to handle Scope in javaScript? We have seen Global Scope, Function Scope, Block Scope and Local Scope etc.