Scope in JavaScript

Scope determines the visibility or accessibility of a variable or other resource in the area of your code.

Global Scope

There’s only one Global scope in the JavaScript document. The area outside all the functions is considered the global scope and the variables defined inside the global scope can be accessed and altered in any other scopes.

Local Scope

Variables declared inside the functions become Local to the function and are considered in the corresponding local scope. Every function has its own scope. The same variables can be used in different functions because they are bound to the respective functions and are not mutual visible.

The local scope can be divided into function scope and block scope.

The concept of block scope is introduced in ECMAScript 6 (ES6) together with the new ways to declare variables — const and let.

Whenever you declare a variable in a function, the variable is visible only within the function. You can’t access it outside the function. var is the keyword to define a variable for function-scope accessibility.

Block scope is the area within if, switch conditions or for and while loops. Generally speaking, whenever you see {curly brackets}, it is a block. In ES6, const and let keywords allow developers to declare variables in the block scope, which means those variables exist only within the corresponding block.

Lexical scope means the children’s scope have the access to the variables defined in the parent scope. The children’s functions are lexically bound to the execution context of their parents.



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Abhay Jain

Abhay Jain

Developer with 3 yrs of industrial experience in developing scalable web applications.