Fetch is browser API ,it is used to make AJAX call to server without disturbing full page of application, it resides in window object of the browser.

Fetch API send a AJAX request with corresponding input request[User provided ] to server then server response to that request.

headers: {
‘Accept’: ‘application/json’,
‘Content-Type’: ‘application/json’
method: “GET”
.then(response => response.json())
.then(json => console.log(json)).catch(err=>console.log(err))

Headers :- provide header information like content-type, Auth -token etc..
Method :- Type of http request like GET , POST ,PUT , DELETE, PATCH etc…
Then and catch :- Both are callbacks, Then executes once request resolves successfully, it may contains multiple then block first then block response is passed to another then block

What is single page Application?

Giving mobile application feeling to web users by updating needed html in the browsers. We can build SPA using javaScript framework like Vuejs, Angular, React etc..

How does it works?

Browser send request to server for SPA, Server sends all javaScript bundles to browser so browser only request for JSON format data from the server if any need. Javascript in browser has an ability to create and update the HTML.

is it slow?

The initial loading of SPA is quite slow because of bundle should download before it loads to users.

Can I reduce Initial loading time of SPA?

Yes, we should go for Hydration.

Build requested page in server and send to browser mean while download the javascript bundle to browser.

Example:- Vuejs has NUXT to solve this problem.

JWT is JSON web token, It has an information about expire date, email etc.., It helps to validate your request once you loggedIn to website. it was issued by server with secrete.

IS JWT Secure?

Yes, You can see the information of jwt but you can’t change the information because server generated jwt…


when you open a website in browser the visible part of screen is User Interface. Browser has an ability to send or receive request from server,It has an engine to execute Javascript. HTML is like a skeleton, Css give style, javascript gives actions.


The huge dynamic data stored in database. The frontend request for data in backend using API.


API is a pice of code helps to interact with database data on the internet.


JSON format has a key value pair data format, it is an efficient data format to transfer data between frontend to backend.


Var keyword has global Or Function scope, it can be re-declared inside its scope, variable should be followed by var.

function varGlobalScope(){
var y=90; // declare
console.log(y); // 90
var y=89;//re-declare
console.log(y) //89


Let keyword has Block scope, It can’t be re-declared and can’t access…

Kishore ks

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