JAVASCRIPT

new promise function

const myPromise = new Promise((resolve, reject) => {
  setTimeout(() => {
    resolve('foo');
  }, 300);
});

myPromise
  .then(handleResolvedA, handleRejectedA)
  .then(handleResolvedB, handleRejectedB)
  .then(handleResolvedC, handleRejectedC);

javascript promise example basic

const anotherPromise = new Promise((resolve, reject) => {
  setTimeout(() => {
    resolve('this is the eventual value the promise will return');
  }, 300);
});

// CONTINUATION
anotherPromise
.then(value => { console.log(value) })

Creating a promise

JS
copy
let done = true

const isItDoneYet = new Promise((resolve, reject) => {
  if (done) {
    const workDone = 'Here is the thing I built'
    resolve(workDone)
  } else {
    const why = 'Still working on something else'
    reject(why)
  }
})

promise in javascript

const studentRol=new Promise((resolve, reject) => {
    setTimeout(()=>{
        /**this function will give the value Of tageted studebt Roll number  */
           let RollOffStd=[1,2,3,4,5,6,7,8];
        
            for (let index = RollOffStd[RollOffStd.length-1]+1 ; index <50; index++) {
                RollOffStd.push(index)
                
            }
            
            resolve( RollOffStd)
            
            reject('My name is Noor mohammad ')
      

    },1000)
})


const mybiodata=(gRollOfStudent /* this is First parameter OF ( mybiodata function ) and You can change parameter value  */)=>{
    return new Promise((resolve, reject) => {
        setTimeout((x) => {
           let  bio={
                myname : 'Noor mohammad Patwary ' ,
                age : 25 ,
            }

            resolve(`my name is ${bio.myname } and my age =  ${bio.age } and my roll is =${x} ` )
        }, 1000,gRollOfStudent);
    })
}

studentRol.then(( RollOfStudent)=>{
    console.log(RollOfStudent); /** From here we are gating the Value OF student roll number  */
    mybiodata(RollOfStudent[1] /* this is First Argument OF ( mybiodata function )*/).then((fff)=>{
        console.log(fff);
    })

}).catch((x)=>{
    console.log(x);
})

promise in javascript

/*
A promise is a building object of JavaScript, using it we can easily do 
asynchronous tasks. Also, the concept that is used to create clean code 
basically promises.
*/
//Promise
let firstPromise = new Promise((resolved, reject) => {
    let fullName = 'Muhammad Shahnewaz';
    setTimeout(() => resolved(fullName), 3000);  //we need to use setTimeout() 
}).then((name) => {
    console.log('I am ' + name);    //Muhammad Shahnewaz
});

Making promises

new Promise((resolve, reject) => {
  if (ok) { resolve(result) }
  else { reject(error) }
})
 

Using Then To Create A Promise In JavaScript

async function abc()
{
Promise.resolve("hello world").then(function(value)
{
	console.log(value);
    }

javascript Program with a Promise

const count = true;

let countValue = new Promise(function (resolve, reject) {
    if (count) {
        resolve("There is a count value.");
    } else {
        reject("There is no count value");
    }
});

console.log(countValue);

Promise in ES6

function makeRequest(method, url) {
  return new Promise((resolve, reject) => {
    let request = new XMLHttpRequest()

    request.open(method, url)
    request.onload = resolve
    request.onerror = reject
    request.send()
  })
}

makeRequest('GET', 'https://url.json')
  .then((event) => {
    console.log(event.target.response)
  })
  .catch((err) => {
    throw new Error(err)
  })

Create A Promise In JavaScript

async function abc() 
{ 	
	const myPromise = new Promise(function(resolve, reject) {
   resolve("hello world");
});
let y= await myPromise;
console.log(y);
/*"hello world*/
	}

promise syntax for javascript

let myPromise = new Promise(function(myResolve, myReject) {
// "Producing Code" (May take some time)

  myResolve(); // when successful
  myReject();  // when error
});

// "Consuming Code" (Must wait for a fulfilled Promise)
myPromise.then(
  function(value) { /* code if successful */ },
  function(error) { /* code if some error */ }
);

Promises in ES6

function asyncFunc() {
    return new Promise((resolve, reject) => {
        setTimeout(() => {
          const result = Math.random();
          result > 0.5 ? resolve(result) : reject('Oppps....I cannot calculate')
        }, 1)
    });
}

for (let i=0; i<10; i++) {
	asyncFunc()
    	.then(result => console.log('Result is: ' + result))
    	.catch(result => console.log('Error: ' + result))
}

javascript Create a Promise

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

promise syntax in js

// make new promise ... so this object will promise us that it will hold an Asynchronous action
// some times promise resolve and some times promise get rejected
const A = new Promise((resolve, reject) => {
    setTimeout(() => {
        // here we pass argument if promise get resolved
        resolve('Done');

        // here we pass argument if promise get rejected
        reject('Didn"t');
    }, 3000);
});


// design handling callback function for resolve 
let handleResolvedA = (massage)=>{console.log(massage)}

// design handling callback function for reject 
let handleRejectedA = (massage)=>{console.log(massage)}


// do handling for both
A.then(handleResolvedA, handleRejectedA)

making promises in js

getData()
    .then(data => console.log(data))
    .catch(error => console.log(error));

promises in javascript

myPromise.then(
  function(value) { /* code if successful */ },
  function(error) { /* code if some error */ }
);

js function that return a promise example

// ? created a function that returns a promise, take a parameter of a boolean
function myPromise(bool) {
  return new Promise((resolve, reject) => {
    if (bool) {
      resolve("I have succeeded");
    } else {
      reject("I have failed");
    }
  });
}

// ? call the function and pass in a boolean
myPromise(true).then((res) => console.log(res));
myPromise(false).then((res) => console.log(res)).catch((err) => console.log(err));

promise in js

myPromise
.then(handleResolvedA)
.then(handleResolvedB)
.then(handleResolvedC)
.catch(handleRejectedAny)
.finally(handleComplition)

javascript promise example

/* Testing Grepper

js promise example

function examplePromise(){
  let promiseToReturn = new Promise(function (resolve, reject) {
    let sum;
    setTimeout(function(){
      sum = 5 + 6;
      if(sum > 10) {
        resolve(sum);
      }else{
        reject('The promise has been rejected');
      }     
    }, 2000);
  });
  return promiseToReturn;
}

console.log('some piece of code');
examplePromise().then(function(result){
  console.log(result);
}).catch(function(error){
  console.log(error);
});
console.log('another piece of code');

JavaScript Promise Methods

Method	Description
all(iterable)	Waits for all promises to be resolved or any one to be rejected
allSettled(iterable)	Waits until all promises are either resolved or rejected
any(iterable)	Returns the promise value as soon as any one of the promises is fulfilled
race(iterable)	Wait until any of the promises is resolved or rejected
reject(reason)	Returns a new Promise object that is rejected for the given reason
resolve(value)	Returns a new Promise object that is resolved with the given value
catch()	Appends the rejection handler callback
then()	Appends the resolved handler callback
finally()	Appends a handler to the promise