1private firstAction():Promise<any> {
2  return new Promise<any>(
3    (resolve, reject) => { ... }
4  );
5}
6private secondAction():Promise<any> {
7  return new Promise<any>(
8    (resolve, reject) => { ... }
9  );
10}
11execute() {
12  this.firstAction().then(
13    (firstResult:any) => this.secondAction().then(
14      (secondResult:any) => { ... }
15    );
16  )
17}

1// base case 
2promise
3  .then(...)
4  .then(...)
5  .then(...)
6  .catch(...)
7
8//real world
9coinflip(10)
10  .then(betAgain)
11  .then(betAgain)
12  .then(betAgain)
13  .then(result => {
14    console.log(`OMG, WE DID THIS! TIME TO TAKE ${result} HOME!`);
15  })
16  .catch(handleRejection);

1new Promise(function(resolve, reject) {
2
3  setTimeout(() => resolve(1), 1000); // (*)
4
5}).then(function(result) { // (**)
6
7  alert(result); // 1
8  return result * 2;
9
10}).then(function(result) { // (***)
11
12  alert(result); // 2
13  return result * 2;
14
15}).then(function(result) {
16
17  alert(result); // 4
18  return result * 2;
19
20});

1const promise2 = doSomething().then(successCallback, failureCallback);
2

1/* Let's break n STEP-BY-STEP (cpy paste n console u'll have clear view)
2
31. Promises chaining will allow us to add many async operations
4 in a sequence way (i.e  in order)
52. But like we have callback hell, here our code at the end 
6will be more difficult to read
73. TIPS : Best options are go with >> {FETCH API, Async/Await} 
84. NOTE : Learn promises once, understand no.3 in a easy way, above
9both completely relay on Promises concept, makesure u understand them
10clearly. */
11
12
13//EXAMPLE
14
15var result = true;
16var learsJS = new Promise((resolve,reject) => {
17  setTimeout(() => {
18    if(result){ //if true resolve below case
19    resolve("This is my 1st resolved case");
20  }
21    else{
22    reject("I need some more time");
23  }
24  }, 2000);
25}).then(resolvedData1 => {
26	console.log(resolvedData1); //resolved promise1 - 5th line
27  return new Promise((resolve) => { // returning another promise2
28    resolve(`${resolvedData1} -- This is 2nd resolved case`)
29  });
30})
31.then(resolvedData2 => {
32  console.log(resolvedData2); //resolved promise2
33	return new Promise((resolve) => { // returning another promise3
34    resolve(` ${resolvedData2} -- This is my 3rd resolved case`)
35  })
36})
37.then(resolvedData3 => {
38  console.log(resolvedData3); //resolved promise3
39	return new Promise((resolve) => { //returning final promise
40    resolve(` ${resolvedData3} -- This is my Final resolved case`)
41  })
42})
43.then(finalData => console.log(finalData)); //resolved final promise