promise catch

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

1We use promise to make a  AsyncFunction, cose simetime we have to wait that function give 
2us some result.
3Example, if we use ajax we have await ajax data or statament.
4_____________________________________
5Make a simple example.
6_____________________________________
7var asyncronus_function= (number)=>
8		{
9			return new Promise( (accept, reject)=>
10			{
11			})
12		}                 
13_____________________________________
14this function return a promise Object, thet required a function executor
15this functions (accept, reject) are defined in the executor 
16function, that was needed in promise constructor.
17Syntax: new Promise (executor)
18executor= (accept, reject) =>{}
19
20if function end well we return a accept(), otherwise reject()
21_____________________________________
22Let complete asyncronus_function
23_____________________________________
24var asyncronus_function= (number)=>
25		{
26			return new Promise( (accept, reject)=>
27			{
28				if(number>10)
29				return accept("my first async");
30				return reject("my first async error")
31			})
32
33		}
34if it dont return any of this 2 function, Promise state is [PENDING] ,
35if return accept is [RESOLVED]  end if return reject is [REJECTED]
36_____________________________________
37how we can retrieve accept or reject?
38_____________________________________
39there is two methods really important, that we have to consider afther we call this function
401) .then(function(error){}) is call when promise state is [RESOLVED]
412) .error(function(error){}) is call when promise state is [REJECTED]
423) do nothing if [PENDING]
43_____________________________________
44let call asyncronus_function()!!! 
45_____________________________________
46	asyncronus_function(MY_NUMBER).then(function(data)
47        {
48			console.log(data)
49    	}).catch(error => 
50        {
51      			console.log(error)
52    	});
53		
54if  MY_NUMBER> 10 ,asyncronus_function print data : OUTPUT my first async
55if MY_NUMBER<10 , asyncronus_function print error : OUTPUT my first async error
56HOPE it halp and have a nice day! 
57
58
59

1// errors that occur in asynchronous code inside promises cannot be caught with regular try/catch
2// you need to pass the error handler into `.catch()`
3
4fetchUserData(userId).then(console.log).catch(handleError);