The document covers a tutorial on JavaScript concepts, including a review of a previous lecture, creation of mini-projects, and explanations of JSON, the event loop, and callback queues. It details the handling of asynchronous JavaScript through concepts like promises, event loop prioritization, and the distinction between REST and GraphQL APIs. Additionally, it explains callback functions and methods for handling asynchronous calls, such as AJAX and promises.

1. Tutorial - 6
• Revision of yesterday lecture
• Create a mini project of a simple calculator
• Create a mini project of todo lis
• What is JSON
• Event loop
• Event loop examples
• callback-queue
• API
• async calls
• setTimeout
• fetch
• Promise

2. Event loop
• Any execution happening in JS is taken care of by its
property of being "single threaded synchronous
language"
• And in order to achieve that we have Execution
Context
• But sometimes we have scenarios of handling the
call back functions or promises where the
behaviour of EC is not regular in order to maintain
JS core value of single threaded + sync. language

3. • Just to achieve that we have something called Event
loop
• Lets look into the pictorial way where is location of JS

4. • Just to highlight one thing that browser instead of
just executing the JS code on client side it has many
other powers also and those powers are called as
Web API, like:

5. Example one

6. Example - 2

7. Example - 3

8. • Call back queue is formed by the call backs
• Micro task ques are formed by Promises &
mutation requestes on DOM
• Micro task queue has higher priority then call
back queue
• They both are entertained by event loop
existing between the call-stack and subsequent
queuing system

9. • Because of higher priority of micro tasks
queue over call back queue, it may sometime
may take really long for micro tasks queue to
finished hence it creates a "STARVATION"
situation in for call back queue
• https://www.youtube.com/watch?v=8aGhZQkoFbQ

10. API - Application programming Interface
• Application:
⚬ A call as a template (interface) to perform any operation is
called as API
• Programming:
⚬ API call is related to any particular operation or a
particular program
• Interface:
⚬ These calls are related to any particular endpoint with any
particular predefined template

12. Types of API: There are 2 major kinds of APIs now days
in market - REST API & GraphQL
• REST are bit heavy and have separate endpoints for
separate operation
• GraphQL is super lite and has only 1 endpoint called
"graphql"

13. • https://www.youtube.com/watch?v=PeAOEAmR0D0

14. Callback functions
• A function getting called up by another
function is called as call back function

15. Asynchronous calls

17. AJAX
AJAX uses XHR requests i.e. XMLHttpRequest

18. Promises

20. Different ways to handle the asynchronous calls
async-await

21. fetch-then