what are the promises in javascript code example

Example 1: 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 */ }
);

Example 2: js promise examples

//Promise to load a file...
//use with openFile(url, fCallback);
//fCallback(fileContents){ //do something with fileContents}
const loadFile = url => {
    return new Promise(function(resolve, reject) {
        //Open a new XHR
        var request = new XMLHttpRequest();
        request.open('GET', url);
        // When the request loads, check whether it was successful
        request.onload = function() {
            if (request.status === 200) {
                // If successful, resolve the promise
                resolve(request.response);
            } else {
                // Otherwise, reject the promise
                reject(Error('An error occurred while loading image. error code:' + request.statusText));
            }
        };
        request.send();
    });
};
const openFile = (url, processor) => {
    loadFile(url).then(function(result) {
            processor(result);
        },
        function(err) {
            console.log(err);
        });
};

Example 3: .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"));
  }
});

Example 4: 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

Example 5: 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));