Promise in ES6
Promise in ES6
xxxxxxxxxxfunction 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) })Source: softhunt.net
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xxxxxxxxxxconst myPromise = new Promise((resolve, reject) => { setTimeout(() => { resolve('foo'); }, 300);});myPromise .then(handleResolvedA, handleRejectedA) .then(handleResolvedB, handleRejectedB) .then(handleResolvedC, handleRejectedC);Source: developer.mozilla.org
xxxxxxxxxx<!DOCTYPE html><html lang="en"><head> <meta charset="UTF-8"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <title>Document</title></head><body> <script> const promise = new Promise((resolve, reject) => { setTimeout(()=>{ let flag = 0; // true fasle 1 or 0 if(!flag){ resolve({name:'Malik Amir Hamza' , id:1}); } else{ reject('error something went wrong'); } },2000); }); promise .then((user)=>{console.log(user)}) .catch((error)=>{console.log(error)});</script> </body></html>Source: Grepper
xxxxxxxxxx//promise is an object that give result of request or reject request//creation of promiseconst promise = new Promise((resolve, reject) => { setTimeout(() => { console.log('got the user'); // resolve({ user: 'shirshak' }); reject(new Error('User not logged in')); }, 2000);});//consume of promisepromise .then(user => { console.log(user); }) .catch(err => console.log(err.message));Source: Grepper
xxxxxxxxxx----------------------------------------Promise.all() allSettled() race()----------------------------------------* Promise.all() : - all() method is used when all promises are expected to return the resolved state. - showing result at a particular follow sequence.// Example: const p1 = new Promise((resolve,reject)=>{ setTimeout(()={ resolve("Promise3"); },2000) );Promise.all([p1,p2,p3]).then((prMsgs)=>{ console.log(prMsgs); }) * Promise.allSettel(): - showing all the result regardless resolve or reject - It will show resolve or reject promises one by one.* Promise.race(): - From the list of promises if any promise returns the result first then it will show that promise result. ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^Promise : //Simple promise example: const data = new Promise((resolve, reject) => { if (1 > 3) { resolve('Working fine') } else { reject('Something wrong') }})data.then((res) => { console.log(`Success=>`, res)})data.catch((err) => { console.log(`Error=>`, err)})Source: Grepper
xxxxxxxxxxconst 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);})Source: Grepper
xxxxxxxxxx/*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.*///Promiselet 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});Source: Grepper
xxxxxxxxxxfunction 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))}Source: softhunt.net
xxxxxxxxxx// 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 rejectedconst 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 bothA.then(handleResolvedA, handleRejectedA)Source: Grepper
xxxxxxxxxxlet promise = new Promise((resolve, reject) => { // Asynchronous operation if (errorOccurred) { reject(new Error("An error occurred.")); } else { resolve(result); }});Source: Grepper
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