Web development basics (Part-5)
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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.
Web development basics (Part-5)
- 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"
- 14. Callback functions • A function getting called up by another function is called as call back function
- 17. AJAX AJAX uses XHR requests i.e. XMLHttpRequest
- 18. Promises
- 20. Different ways to handle the asynchronous calls async-await
- 21. fetch-then