Skip to main content

Clarification needed on how catch() works in a Promise chain with multiple .then() calls

I am new to Javascript and need a clarification about using catch() in a Promise Chain. I have read multiple articles that simply state that a catch() at the end of a promise chain will handle an error from any of the .then() calls preceding it. I have also read that a .then(function(result)) will not be called if invoked on a rejected promise. So I can't understand how catch() at the end of a promise chain can catch an error without each .then() in between returning a rejected promise one after the another until it reached the .catch() part of it.

I wrote a piece of code that leads me to think that after an error is thrown from a .then(), each interim .then() then returns a rejected promise until it reaches the catch() part of the promise chain. I would like to know if I am getting this picture accurately.

<!DOCTYPE html>
<script>
"use strict";

let promise = new Promise(function(resolve, reject) {
  resolve("promise result");
})

// then1 holds a rejected promise
let then1 = promise.then(function(result) {
  alert("inside then1");
  return new Promise((resolve, reject) => {
    reject(new Error("hi error"));
  });
})

// The alert never displays so undertandably function(result) is not invoked
let then2 = then1.then(function(result) {
  alert("inside then2");
})

// then2.then() works leading me to believe then1.then() above did return a rejected promise
then2.then(function(result){
  alert("inside then2_result");
  alert(result);
  }, function(error){
  alert("inside then2_error");
  alert(error);
});
</script>
Via Active questions tagged javascript - Stack Overflow https://ift.tt/s9FjxnQ
Labels:

Comments

Post a Comment

Popular posts from this blog

How to show number of registered users in Laravel based on usertype?

i'm trying to display data from the database in the admin dashboard i used this: <?php use Illuminate\Support\Facades\DB; $users = DB::table('users')->count(); echo $users; ?> and i have successfully get the correct data from the database but what if i want to display a specific data for example in this user table there is "usertype" that specify if the user is normal user or admin i want to user the same code above but to display a specific usertype i tried this: <?php use Illuminate\Support\Facades\DB; $users = DB::table('users')->count()->WHERE usertype =admin; echo $users; ?> but it didn't work, what am i doing wrong? source https://stackoverflow.com/questions/68199726/how-to-show-number-of-registered-users-in-laravel-based-on-usertype
Post a Comment
Read more

Why is my reports service not connecting?

I am trying to pull some data from a Postgres database using Node.js and node-postures but I can't figure out why my service isn't connecting. my routes/index.js file: const express = require('express'); const router = express.Router(); const ordersCountController = require('../controllers/ordersCountController'); const ordersController = require('../controllers/ordersController'); const weeklyReportsController = require('../controllers/weeklyReportsController'); router.get('/orders_count', ordersCountController); router.get('/orders', ordersController); router.get('/weekly_reports', weeklyReportsController); module.exports = router; My controllers/weeklyReportsController.js file: const weeklyReportsService = require('../services/weeklyReportsService'); const weeklyReportsController = async (req, res) => { try { const data = await weeklyReportsService; res.json({data}) console...
Post a Comment
Read more

How to split a rinex file if I need 24 hours data

Trying to divide rinex file using the command gfzrnx but getting this error. While doing that getting this error msg 'gfzrnx' is not recognized as an internal or external command Trying to split rinex file using the command gfzrnx. also install'gfzrnx'. my doubt is I need to run this program in 'gfzrnx' or in 'cmdprompt'. I am expecting a rinex file with 24 hrs or 1 day data.I Have 48 hrs data in RINEX format. Please help me to solve this issue. source https://stackoverflow.com/questions/75385367/how-to-split-a-rinex-file-if-i-need-24-hours-data
Post a Comment
Read more