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Asynchronous Programming

  • In synchronous programming, the code runs from top of the file to the bottom in a single thread
  • In asynchronous programming, the code runs from the top of the file to the bottom but if it encounters some asynchronous pieces of code in file, a new thread will be given to execute each asynchronous task whereas the main thread continues executing the main code.
  • A file containing asynchronous tasks will run in multiple threads (multi-threading). So, if a some task is taking some time to execute, it will not block other asynchronous tasks or the main code.
  • Because each asynchronous task is handled by a separate thread, the code may not execute in order. attachments/Pasted image 20220603182929.jpg


  • A callback is a function passed as an argument to another function which the calling function can invoke once it has done some task. ```JS const order = (production: Function) => { console.log('Order placed, calling production...') production() }

const production = () => { console.log('Starting production') }

// call the order function and tell what to do once the order is placed order(production); ```

  • If we have multiple steps, each with a callback, then the resulting code has a ladder like appearance. This is called as the callback hell. To overcome this, we use promises and async-await syntax.
    • attachments/Pasted image 20220613194732.jpg


Asynchronous JS | YouTube
Asynchronous Vs Synchronous Programming - YouTube

Last updated: 2022-06-13