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Inbuilt Promises

• Here we just defined a standard promise which will always be in the pending state.

function promiseExecutor() {
  setTimeout(() => {
    console.log("Inside promise executor function");
  }, 10000);
}

var promise1 = new Promise(); // calls the Promise() constructor function and create new onject of type "Promise"
var promise1WithExecutor = new Promise(promiseExecutor); 

• In order to resolve and reject the promise, the executor function needs to have resolve and reject functions as arguments and call them appropriately.

// Resolve the promise
var promise1WithExecutor = new Promise(promiseExecutor);
function promise1Executor(resolve, reject) {
  setTimeout(() => {
    resolve();
    console.log("Inside promise executor function");
  }, 2000);
}

// Handle the response of promise using then
promise1WithExecutor.then((someValue) => {
  responseValue = someValue;
});

// Reject the promise
var promise2WithExecutor = new Promise(promiseExecutor);
function promise2Executor(resolve, reject) {
  setTimeout(() => {
    reject();
    console.log("Inside promise executor function");
  }, 2000);
}

// Handle the response of promise using catch
promise2WithExecutor.catch((someValue) => {
  responseValue = someValue;
});

Promises home

Custom Promises

References