Asynchronous JavaScript

Intervals and Timers

setInterval()

The setInterval() method calls a function at specified intervals (in millisecond). The setInterval() method continues calling the function until the clearInterval() is called, or the window is closed.

clearInterval()

The clearInterval() method clears a timer set with the setInterval() method.

setTimeout()

The setTimeout() method calls a function after a number of milliseconds. The setTimeout() a executed only once.

clearTimeout()

The clearTimeout() method clears a timer set with the setTimeout() method.

Difference between Asynchronous and Synchronous

Synchronous JavaScript

Synchronous JavaScript is one in which the code is executed line by line and their tasks are completed instantly, i.e. there is no time delay in the completion of the tasks for those lines of code.

Asynchronous JavaScript

Asynchronous JavaScript is one in which some lines of code take time to run. These tasks are run in the background while the JavaScript engine keeps executing other lines of code. When the result of the asynchronous tasks gets available, is then used in the program.

Callbacks

A Callback is a function that is to be executed after another function has finished executing. Any function that is passed as an argument is called a Callback function.

Callback Helll

This is a big issued caused by coding with complex nested callbacks. Here, each and every callback takes an argument that is a result of the previous callbacks. The code structure looks like a pyramid, making it difficult to read and maintain. Also, if there is an error in one function, then all other function get affected.

Promises

Promises are objects that either return the successfully fetched data, or the error. Promises are alternative to callbacks for delivering the result of asynchronous computation. They are more readable as compared to Callbacks.

Async/Await

The keyword async is used to make a function asynchronous. The await keyword will ask the execution to wait until the defined task gets executed. It allows the use of await keyword inside the functions with async keyword.