What is the promise & Call back in javascript

I read multiple definitions for the callback and promise which confuse beginners so in this article I am giving one of them with examples.

Promise

A promise is an object which is capable to handle non-blocking events means a Promise can handle asynchronous functions in synchronous form.

How promise works:- It will work in 3 possible states.

• pending: initial state, neither fulfilled nor rejected.
• fulfilled: meaning that the operation was completed successfully.
• rejected: meaning that the operation failed.

Example:-

const pro = new Promise((resolve, reject) => {
  setTimeout(function() {
    resolve("Promise resolved");
  }, 1000);
})

pro.then(data => {
  console.log("Data->", data);
}).catch(error => {
  console.log("Error->", error);
})

Callback

A callback is passed as an argument to another function so that it can be executed in that other function is called as a callback function.

Example 1:-

const callback = function(sum){
  console.log("Sum of a and b =", sum);  
}

function sum(a,b,callback){
  let sum = a+b;
  callback(sum);
}

sum(2,3, callback);

Example 2:-

const callback = function(sum){
  console.log("Sum of a and b =", sum);  
}

setTimeout(callback, 1000, 5);

That’s it for this time! I hope you enjoyed this post. As always, I welcome questions, notes, comments and requests for posts on topics you’d like to read. See you next time! Happy Coding !!!!!