Callback , Async , Await , Promise

Callback, Promises, and Async-await are a way to deal with asynchronous data. Asynchronous programming in JavaScript is a way in which the program doesn’t wait until the execution of something is going on.

Asynchronous vs. Synchronous:

In synchronous operations tasks are performed one at a time and only when one is completed, the following is unblocked. In other words, you need to wait for a task to finish to move to the next one.

In asynchronous operations, on the other hand, you can move to another task before the previous one finishes.

1.Callbacks

A callback is a function that is passed to another function. When the first function is done, it will run the second function.

Example:-
function callNames(){ console.log("Sam");  
 setTimeout(() => { console.log("Sai"); }, 300);  
console.log("Jai")}
callNames();// Sam  Sai Jai

2.Async

It simply allows us to write promises based code as if it was synchronous and it checks that we are not breaking the execution thread. It operates asynchronously via the event-loop. Async functions will always return a value. It makes sure that a promise is returned and if it is not returned then JavaScript automatically wraps it in a promise which is resolved with its value.

3.Await

Await function is used to wait for the promise. It could be used within the async block only. It makes the code wait until the promise returns a result. It only makes the async block wait.

Syntax
async function name(){
// await statement
}

Example:-
function timing(){
return new Promise(resolve=>{
setTimeout(()=>{
resolve("printing the correct answer")
},3000);
})
}
async function asyncOutput(){
const result=await timing()
console.log(result);
} 
asyncOutput();//printing the correct answer

4.Promises

A promise in JavaScript is similar to a promise in real life. When we make a promise in real life, it is a guarantee that we are going to do something in the future. Because promises can only be made for the future.A promise has two possible outcomes: it will either be kept when the time comes, or it won’t.

A Promise has four states:

fulfilled: Action related to the promise succeeded

rejected: Action related to the promise failed

pending: Promise is still pending i.e. not fulfilled or rejected yet

settled: Promise has fulfilled or rejected

Syntax
 const promise= new Promise (function(resolve,reject){
//do something
});


Example:-
const promise=new Promise((resolve,reject)=>{
  setTimeout(()=>resolve("resolve means the code will run"),5000)

});

promise.then((promise)=>console.log("then means the code is correct",promise))
.catch((promise)=>console.log("catch means the code is incorrect",promise))
.finally(()=>console.log("finally means the code is correct or incorrect return something",))
//then means the code is correct resolve means the code will run
 finally means the code is  correct or incorrect return something.

Let's we see on next Blog...

Thank you...