Loading Please Wait...
Scope determines the accessibility of variables, objects, and functions from different parts of the code.
JavaScript has 3 types of scope:
Variables declared inside a { } block cannot be accessed from outside the block.
{
let name = "Lynxsia";
}
// name can NOT be used here
Variables declared with the var keyword can NOT have block scope and can be accessed from outside the block.
{
var name = "Lynxsia";
}
// name CAN be used here
Variables declared within a JavaScript function, become LOCAL to the function.
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.
// code here can NOT use name
function myFunction() {
let name = "Lynxsia";
// code here CAN use name
}
// code here can NOT use name
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.
function myFunction1() {
var name = "Lynxsia"; // Function Scope
}
function myFunction2() {
let name = "Lynxsia"; // Function Scope
}
function myFunction3() {
const name = "Lynxsia"; // Function 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.
A variable declared outside a function, becomes GLOBAL. All scripts and functions on a web page can access it.
var name = "Lynxsia"; // Global Scope
let name = "Lynxsia"; // Global Scope
const name = "Lynxsia"; // Global Scope
If you assign a value to a variable that has not been declared, it will automatically become a GLOBAL variable.
myFunction();
// code here can use name
function myFunction() {
name = "Volvo";
}
All modern browsers support running JavaScript in "Strict Mode". In "Strict Mode", undeclared variables are not automatically global.
In HTML, the global scope is the window object. We can access global variable (only var not let and const) via window object.
var name = "Volvo"; // code here can use window.name
let name = "Volvo"; // code here can not use window.name
const name = "Volvo"; // code here can not use window.name
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 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).
How you feel about this blog:
Share this blog on:
If you find any error in the turtorials, or want to share your suggestion/feedback, feel free to send us email at: info@lynxsia.com
Contact Us
We are concern with various development process like website design & development, E-commerce development, Software development, Application development, SMS & Bulk SMS Provider, PWA Development, and many more..
Copyright © , Lynxsia IT Solutions, All rights reserved