JAVASCRIPT

javascript promise

let conditions=true;


const proms= new Promise((resolve, reject) => {
    setTimeout(() => {
        if (conditions) {
            resolve ("Hello")
        } else {
            reject ("This condition faild")
        }
    }, 2000);
});


proms.then((result) => {
    console.log(result);
})
.catch(function(error){
    console.log(error);
});

javascript promise

var promise = new Promise(function(resolve, reject) {
  // do some long running async thing…
  
  if (/* everything turned out fine */) {
    resolve("Stuff worked!");
  }
  else {
    reject(Error("It broke"));
  }
});

//usage
promise.then(
  function(result) { /* handle a successful result */ },
  function(error) { /* handle an error */ }
);

what is promise in javascript

Promises are used to handle asynchronous operations in JavaScript.
They are easy to manage when dealing with multiple asynchronous operations
where callbacks can create callback hell leading to unmanageable code.

promise

new Promise( (res, rej) => {
  setTimeout(() => res(1), 1000);
}).then( (res) => {
  console.log(res); // 1
  return res*2
}).then( (res) => {
  console.log(res); // 2
});

javascript promise

let promise = new Promise((resolve,reject)=>{
                try {
                    resolve("some data");
                } catch (error) {
                    reject(error);
                }
            })
            
            promise.then(function (data) {
                console.log(data);
            },function (error) {
                console.error(error);
            })

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
});

promise javascript

let promise = new Promise(function(resolve, reject){
  try{
  	resolve("works"); //if works
  } catch(err){
    reject(err); //doesn't work
  }
}).then(alert, console.log); // if doesn't work, then console.log it, if it does, then alert "works"

promise js

We use promise to make a  AsyncFunction, cose simetime we have to wait that function give 
us some result.
Example, if we use ajax we have await ajax data or statament.
_____________________________________
Make a simple example.
_____________________________________
var asyncronus_function= (number)=>
		{
			return new Promise( (accept, reject)=>
			{
			})
		}                 
_____________________________________
this function return a promise Object, thet required a function executor
this functions (accept, reject) are defined in the executor 
function, that was needed in promise constructor.
Syntax: new Promise (executor)
executor= (accept, reject) =>{}

if function end well we return a accept(), otherwise reject()
_____________________________________
Let complete asyncronus_function
_____________________________________
var asyncronus_function= (number)=>
		{
			return new Promise( (accept, reject)=>
			{
				if(number>10)
				return accept("my first async");
				return reject("my first async error")
			})

		}
if it dont return any of this 2 function, Promise state is [PENDING] ,
if return accept is [RESOLVED]  end if return reject is [REJECTED]
_____________________________________
how we can retrieve accept or reject?
_____________________________________
there is two methods really important, that we have to consider afther we call this function
1) .then(function(error){}) is call when promise state is [RESOLVED]
2) .error(function(error){}) is call when promise state is [REJECTED]
3) do nothing if [PENDING]
_____________________________________
let call asyncronus_function()!!! 
_____________________________________
	asyncronus_function(MY_NUMBER).then(function(data)
        {
			console.log(data)
    	}).catch(error => 
        {
      			console.log(error)
    	});
		
if  MY_NUMBER> 10 ,asyncronus_function print data : OUTPUT my first async
if MY_NUMBER<10 , asyncronus_function print error : OUTPUT my first async error
HOPE it halp and have a nice day! 

js promise

const executorFunction = (resolve, reject) => {
  if (someCondition) {
      resolve('I resolved!');
  } else {
      reject('I rejected!'); 
  }
}
const myFirstPromise = new Promise(executorFunction);

javascript promise

const myScore=500 ;

function checkNumnbner() {
    console.log('Course Enrolment Process');
    const myPromise=new Promise((resolve , reject)=>{
        if (myScore >= 80) {
            resolve("First one is true");
        }else{
            setTimeout(() => {
                reject("SORRY we CANT offering you a job")
            }, 2000);
        }
     })
    return myPromise;
    
}

function offerLater() {
    const newPromise2=new Promise((resolve) => {
        setTimeout(() => {
            resolve("congratulation we are offering you a job")
        }, 500);
        
    })
    return newPromise2;
}

function thanksT() {
    const End= new Promise(() => {
        
           setTimeout(()=>{
            console.log(('Thanks to try'));
           },2000)
        
    })
    return End
}

checkNumnbner()
.then(offerLater)
.then(value=> console.log(value))
.then(thanksT)

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

promise

const myPromise = new Promise((resolve, reject) => {  
    let condition;  
    
    if(condition is met) {    
        resolve('Promise is resolved successfully.');  
    } else {    
        reject('Promise is rejected');  
    }
});

promise javascript

/*
Promise is a constructor function, so you need to use the new keyword to 
create one. It takes a function, as its argument, with two parameters - 
resolve and reject. These are methods used to determine the outcome of the
promise. 
The syntax looks like this:
*/

const myPromise = new Promise((resolve, reject) => {

});

js promise API

const fetchData = () => {
  fetch('https://api.github.com').then(resp => {
    resp.json().then(data => {
      console.log(data);
    });
  });
};

promise javascript

let num = 10;
//call back function
const promis = new Promise(function (resolve, reject) {

  if (num > 5) {

    //this resolve method will send data to resoleveData variable
    resolve(" Problem resolved successfully")
  }
  else {
    //this reject method will send data to rejectData variable
    reject("sorry problem couldn't solve")
  }

})
//resoleveData variable
promis.then(function (resolveData) {

  console.log(resolveData)
  //rejectData variable
}).catch(function (rejectData) {

  console.log(rejectData)
})

js promise

const prom = new Promise((resolve, reject) => {
  resolve('Yay!');
});
 
const handleSuccess = (resolvedValue) => {
  console.log(resolvedValue);
};
 
prom.then(handleSuccess); // Prints: 'Yay!'

javascript promises

var posts = [
  {name:"Mark42",message:"Nice to meet you"},
  {name:"Veronica",message:"I'm everywhere"}
];

function Create_Post(){
  setTimeout(() => {
    posts.forEach((item) => {
      console.log(`${item.name} --- ${item.message}`);
    });
  },1000);
}

function New_Post(add_new_data){
  return new Promise((resolve, reject) => {
    setTimeout(() => {
     posts.push(add_new_data);
      var error = false;
      if(error){
        reject("Something wrong in </>, Try setting me TRUE and check in console");
      }
      else{
        resolve();
      }
    },2000);
  })
}

New_Post({name:"War Machine",message:"I'm here to protect"})
    .then(Create_Post)
    .catch(err => console.log(err));

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)

js promises

let examplePromise = 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);
});

promise javascript

const promiseA = new Promise( (resolutionFunc,rejectionFunc) => {
    resolutionFunc(777);
});
// At this point, "promiseA" is already settled.
promiseA.then( (val) => console.log("asynchronous logging has val:",val) );
console.log("immediate logging");

// produces output in this order:
// immediate logging
// asynchronous logging has val: 777

Promise

let doSecond = () => {
  console.log('Do second.')
}

let doFirst = new Promise((resolve, reject) => {
  setTimeout(() => {
    console.log('Do first.')

    resolve()
  }, 500)
})

doFirst.then(doSecond)

promise js

A promise is an object that may produce a single value some time in the future: 
either a resolved value, or a reason that it’s not resolved 

javascript promise

var myImage = document.querySelector('#example');

function loaded() {
  // bien, la imagen cargó
}

if (myImage.complete) {
  loaded();
} else {
  myImage.addEventListener('load', loaded);
}

myImage.addEventListener('error', function() {
  // ocurrió un imprevisto
});

promise

conts trypromises= new Promise((resolve,reject)=>{
	reject()	
  resolve()
});

trypromises.then((data)=>{
	console.log(data)
}).then()

----------------------------------
const proses=(aa)=>{
	return new Promise((resolve,reject)=>{
      	reject()
    	resolve()
    })
};

js promise

let num = 2;
//call back function
const promis = new Promise(function (resolve, reject) {

  if (num > 5) {

    //this resolve method will send data to resoleveData variable
    resolve(" Problem resolved successfully")
  }
  else {
    //this reject method will send data to rejectData variable
    reject("sorry problem couldn't solve")
  }

})

promis.then(
    //resoleveData variable
    function (resolveData) {

    console.log(resolveData)
    
    }).catch(
    //rejectData variable
    function (rejectData) {

        console.log(rejectData)
    })

promise

<script>
    var promise = Promise.resolve(17468);
 
promise.then(function(val) {
    console.log(val);
});
//Output: 17468
</script>

promise in js

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

javascript promises

let dataIsLoading = true;

promise
  .then(data => {
    // do something with data
  })
  .catch(error => {
   // do something with error
  })
  .finally(() => {
    dataIsLoading = false;
  })

what is promise in javascript

Promises make async javascript easier as they are easy to use and write than callbacks. Basically , promise is just an object , that gives us either success of async opertion or failue of async operations

promise js

A Promise is in one of these states:

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

javascript promise

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

maPromesse
  .then(gestionnaireSuccesA, gestionnaireEchecA)
  .then(gestionnaireSuccesB, gestionnaireEchecB)
  .then(gestionnaireSuccesC, gestionnaireEchecC);

promise

<script>
    var promise = Promise.resolve(17468);
 
promise.then(function(val) {
    console.log(val);
});
//Output: 17468
</script>

JavaScript Promises

// returns a promise
let countValue = new Promise(function (resolve, reject) {
   reject('Promise rejected'); 
});

// executes when promise is resolved successfully
countValue.then(
    function successValue(result) {
        console.log(result); // Promise resolved
    },
 )

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