JavaScript: Promise

How to use JavaScript Promises in the industry :-

Ecommerce:

Promises are a way to handle asynchronous operations more cleanly and manage errors effectively.

• E-commerce platforms often rely on external APIs for various functionalities like product catalog, payment processing, or shipping calculations. When making API requests, use the fetch API or a library like Axios that returns promises.

fetch('https://api.example.com/products')
  .then(response => response.json())
  .then(data => {
    // Handle the API response data
  })
  .catch(error => {
    // Handle errors
  });

• Promises are a fundamental concept in asynchronous programming in JavaScript.

• They provide a way to handle asynchronous operations more cleanly and manage the flow of asynchronous code.

****The core concepts of promises include:

1. States:

   • Promises have three possible states:
     • Pending: The initial state when a promise is created, representing that the operation is ongoing or hasn't completed yet.
     • Fulfilled: The state when the asynchronous operation is successfully completed, and a result value is available.
     • Rejected: The state when the asynchronous operation encounters an error or fails, and an error reason is provided.

2. Callbacks:

   • Promises use two callback functions to handle their states:
     • resolve(): A function called when the promise is successfully fulfilled. It passes a result value to any attached .then() handlers.
     • reject(): A function called when the promise is rejected due to an error. It passes an error reason to any attached .catch() handlers.

3. Chaining:

   • Promises allow you to chain multiple asynchronous operations together using .then(). This enables you to specify a sequence of tasks to execute when the promise is fulfilled.

   someAsyncFunction()
     .then(result => {
       // Handle the result
       return anotherAsyncFunction(result);
     })
     .then(finalResult => {
       // Handle the final result
     })
     .catch(error => {
       // Handle errors from any of the steps
     });

1. Error Handling:
   • Promises provide a centralized way to handle errors using .catch(). Errors thrown in any .then() block will propagate down to the nearest .catch() handler.

   someAsyncFunction()
     .then(result => {
       // Handle the result
       throw new Error('An error occurred');
     })
     .catch(error => {
       // Handle the error
     });

1. Promise.all():
   • You can use Promise.all() to wait for multiple promises to fulfill in parallel. It resolves when all the provided promises have resolved, providing an array of their results.

   const promises = [promise1, promise2, promise3];
   Promise.all(promises)
     .then(results => {
       // Handle the results
     })
     .catch(error => {
       // Handle errors from any of the promises
     });

1. Async/Await (ES6 and later):
   • ES6 introduced the async/await syntax, which simplifies working with promises, making asynchronous code look more like synchronous code.

   async function fetchData() {
     try {
       const result = await someAsyncFunction();
       // Handle the result
     } catch (error) {
       // Handle errors
     }
   }

Promises are a crucial part of modern JavaScript and are widely used in web development for handling asynchronous operations such as AJAX requests, file I/O, and more. They promote cleaner, more maintainable code by providing a structured way to deal with asynchronous behavior and errors.