1/*
2	A Promise is a proxy for a value not necessarily known when the promise is created. 
3    It allows you to associate handlers with an asynchronous action's eventual success 
4    value or failure reason.
5*/            
6let promise = new Promise((resolve , reject) => {
7  fetch("https://myAPI")
8    .then((res) => {
9      // successfully got data
10      resolve(res);
11    })
12    .catch((err) => {
13      // an error occured
14      reject(err);
15    });          
16});

1new Promise( (res, rej) => {
2  setTimeout(() => res(1), 1000);
3}).then( (res) => {
4  console.log(res); // 1
5  return res*2
6}).then( (res) => {
7  console.log(res); // 2
8});
9

1// base case
2const promise = new Promise(executor);
3
4// more complex example
5const coinflip = (bet) => new Promise((resolve, reject) => {
6  const hasWon = Math.random() > 0.5 ? true : false;
7  if (hasWon) {
8    setTimeout(() => {
9      resolve(bet * 2);
10    }, 2000);
11  } else {
12    reject(new Error("You lost...")); // same as -> throw new Error ("You lost ...");
13  }
14});

1var promise = new Promise(function(resolve, reject) {
2  // do some long running async thing…
3  
4  if (/* everything turned out fine */) {
5    resolve("Stuff worked!");
6  }
7  else {
8    reject(Error("It broke"));
9  }
10});
11
12//usage
13promise.then(
14  function(result) { /* handle a successful result */ },
15  function(error) { /* handle an error */ }
16);

1let promise = new Promise(function(resolve, reject){
2  try{
3  	resolve("works"); //if works
4  } catch(err){
5    reject(err); //doesn't work
6  }
7}).then(alert, console.log); // if doesn't work, then console.log it, if it does, then alert "works"

1myPromise
2.then(handleResolvedA)
3.then(handleResolvedB)
4.then(handleResolvedC)
5.catch(handleRejectedAny)
6.finally(handleComplition)
7