Promise Use Cases In JavaScript

Promise Use Cases In JavaScript

1. Loading Data from an API

  .then(response => response.json())
  .then(data => console.log(data))
  .catch(error => console.error("Failed to load data", error));

Use Case: Fetch data from a remote server and process it when available.

2. File Reading in Node.js

const fs = require('fs').promises;

fs.readFile('example.txt', 'utf8')
  .then(data => console.log(data))
  .catch(error => console.error("Failed to read file", error));

Use Case: Read a file without blocking the main thread, processing its content upon completion.

3. Waiting for Multiple Requests to Complete

]).then(responses => {
  return Promise.all( => res.json()));
}).then(data => console.log(data));

Use Case: Execute multiple API calls simultaneously and wait for all of them to complete.

4. User Authentication

function loginUser(email, password) {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      if (email === '' && password === 'password123') {
        resolve({ userId: 1, profile: "User Profile" });
      } else {
        reject(new Error("Authentication failed"));
    }, 1000);

Use Case: Simulate user login, resolving on success and rejecting on failure.

5. Data Processing Pipeline

  .then(response => response.json())
  .then(data => processData(data))
  .then(processedData => console.log(processedData))
  .catch(error => console.error("Failed in processing pipeline", error));

function processData(data) {
  // Process data
  return modifiedData;

Use Case: Chain operations where each step depends on the successful completion of the previous one.

6. Image Loading

function loadImage(url) {
  return new Promise((resolve, reject) => {
    const image = new Image();
    image.onload = () => resolve(image);
    image.onerror = () => reject(new Error('Failed to load image'));
    image.src = url;

Use Case: Load an image and perform actions once it is fully loaded or handle errors if it fails to load.

7. Asynchronous Loops

async function processArray(array) {
  for (const item of array) {
    await processItem(item);

Use Case: Sequentially process items in an array, waiting for each asynchronous operation to complete before continuing.

8. Database Queries in Node.js

const { Pool } = require('pg');
const pool = new Pool();

pool.query('SELECT * FROM users WHERE id = $1', [1])
  .then(res => console.log(res.rows[0]))
  .catch(e => console.error('Query error', e.stack));

Use Case: Execute a database query and process the results asynchronously.

9. Timeouts

function delay(ms) {
  return new Promise(resolve => setTimeout(resolve, ms));

delay(1000).then(() => console.log("Delayed for 1 second"));

Use Case: Execute some action after a delay, without blocking the main thread.Animation Sequence

10. Animation Sequences

function animateElement(element, animation) {
  return new Promise(resolve => {
    element.addEventListener('animationend', resolve, { once: true });

Use Case: Perform animations on elements sequentially, waiting for one to finish before starting another.

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