What is Promise - TechFliez Academy

The promise is used to handle async operation and its resulting value will be success or failure.
A Promise has basically three state
pending: initial state, neither fulfilled nor rejected.

fulfilled: meaning that the operation completed successfully.
it uses the resolve method for this

rejected: meaning that the operation failed.
it is use reject method for this.


function checkPostiveNumber (number) {
 
  return new Promise((resolve, reject) => {

  try { 
         if((number<0))
         {
            throw new Error(` ${number} is not a postive number` );
         } 
        } catch(msg) {
            reject(`Error in callback ${msg}`); 
        }

        resolve(`${number} is a positive number`)
});
}

let data=checkPostiveNumber(1);
console.log(data);

Promise {: "1 is a postive number"}
__proto__: Promise
[[PromiseStatus]]: "resolved"
[[PromiseValue]]: "1 is a postive number"

C# Dictionary – Interview Questions

Q 1: What is a Promise?

Ans: A Promise represents the eventual result of an asynchronous operation.

Q 2: What are Promise states?

Ans: Pending, Fulfilled, and Rejected.

Q 3: Why use Promises?

Ans: To handle async operations more cleanly than callbacks.

Q 4: What is then() used for?

Ans: To handle successful Promise resolution.

Q 5: What is catch() used for?

Ans: To handle Promise errors.