js promise

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});

1function doSomething() {
2  return new Promise((resolve, reject) => {
3    console.log("It is done.");
4    // Succeed half of the time.
5    if (Math.random() > .5) {
6      resolve("SUCCESS")
7    } else {
8      reject("FAILURE")
9    }
10  })
11}
12
13const promise = doSomething(); 
14promise.then(successCallback, failureCallback);

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//create a Promise
2var p1 = new Promise(function(resolve, reject) {
3  resolve("Success");
4});
5
6//Execute the body of the promise which call resolve
7//So it execute then, inside then there's a throw
8//that get capture by catch
9p1.then(function(value) {
10  console.log(value); // "Success!"
11  throw "oh, no!";
12}).catch(function(e) {
13  console.log(e); // "oh, no!"
14});
15

1const executorFunction = (resolve, reject) => {
2  if (someCondition) {
3      resolve('I resolved!');
4  } else {
5      reject('I rejected!'); 
6  }
7}
8const myFirstPromise = new Promise(executorFunction);

1const prom = new Promise((resolve, reject) => {
2  resolve('Yay!');
3});
4 
5const handleSuccess = (resolvedValue) => {
6  console.log(resolvedValue);
7};
8 
9prom.then(handleSuccess); // Prints: 'Yay!'