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

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"

1/*
2Promise is a constructor function, so you need to use the new keyword to 
3create one. It takes a function, as its argument, with two parameters - 
4resolve and reject. These are methods used to determine the outcome of the
5promise. 
6The syntax looks like this:
7*/
8
9const myPromise = new Promise((resolve, reject) => {
10
11});
12
13

1const promiseA = new Promise( (resolutionFunc,rejectionFunc) => {
2    resolutionFunc(777);
3});
4// At this point, "promiseA" is already settled.
5promiseA.then( (val) => console.log("asynchronous logging has val:",val) );
6console.log("immediate logging");
7
8// produces output in this order:
9// immediate logging
10// asynchronous logging has val: 777
11