Hello friends!! this blog is about fetch() function. I tried my best to put my understanding into words.
It is subdivided into various parts for better understanding.

what is fetch() ?
how it is used ?
what is promise?

what is fetch()?

In fetch() we just pass the url (https) to the function and it gives you the data from the server. fetch() used to make the request to the server and handel the response from the server.
syntax:
var url= "https://abc.com"

fetch(url)
.then(response =>response.json())
.then(json =>console.log(json))
OR
fetch(url)
.then(function responseHandler (response){
return response.json()
})
.then(function jsonHandler(json){
return console.log(json)
})

Here, the "responseHandler","response", "jsonHandler","json" are the function name and the parameter name .we can name it anything but to maintain a standard we write in this form. So to make it more convinent to read we write using the arrow function.

how it is used?

The fetch is used to make a request to the server and handel the response from the server.
now while we fetch you might get a bit confused in why we used two function i.e two then.

First then ,
.then(response=> response.json())
This function takes the particular response from the server including body, headers,status, clone, formData, constructor...etc. what does "response.json()"do??
Convert that data in the json format and give that data to second then.

Second then ,
.then((json)=> console.log(json))
This function takes all the data in the from of json and prints the data in the console.

what is promise?

If i don't talk about promise it would be unfair. promise are like the normal we use in real world.It takes the url and give you and empty promise till when the response from the server is not completed. After a while this promise can have certain state.
There are three types of state in promise:

pending: This is time while request is given.

resolved: It gives particular response back from the server.

rejected: this comes when your request is rejected

For Example

we want to fetch an api

var url ="https://abcd.com"
fetch(url)
.then(function responseHandler (response){
return response.json()
})
.then(function jsonHandler(json){
return console.log(json)
})
Here, it will fetch the data of the API i.e the url which we have given.
It will take all the data in the json format and will give to us.