Introduction

Asynchronous operations are common in the dynamic field of JavaScript development. Efficiently handling these asynchronous operations is essential to guaranteeing seamless and responsive online applications. Promises are a potent weapon in the JavaScript toolbox for managing asynchronous processes. Promises offer a methodical approach to handling asynchronous operations and their results, whether they are successful or unsuccessful. We'll explore the foundations of making promises, chaining them for smooth operation, and gracefully resolving mistakes in this post. Let's set out to become experts in JavaScript promise construction, chaining, and error management.

Recognizing the Creation of Promises

It's critical to understand the producer-consumer connection when working with promises. A promise object is created by the producer, and the consumer manages whether the promise is eventually fulfilled or not.

Making a Promise

We use the built-in Promise constructor in JavaScript to create a promise. We may handle success and failure scenarios with this constructor, which takes a callback function with resolve and reject parameters.

const cart = ["pen", "bottle", "book"];

const promise = createorder(cart);

promise.then(function (orderid) {
    console.log(orderid);
    // proceedtopayment(orderid);
});   
//here, now if we invoke/call the promise with new keyword and passing the functions 
// with parameters (resolve and reject) and eventually returning it...this is a perfectly valid promise.
function createorder(cart) {
    const pr = new Promise(function (resolve, reject) {
// Logic to validate and process the cart...
        if (!validateorder()) {
            const err = new Error("data not found");
            reject(err);
        }
        const orderid = "12345"; // orderid will be called from database...
        if (orderid) {
//here, we can also use settimeout to delay the output(RESOLVE SECTION)
            resolve(orderid);
        }
    });
    return pr;
}
function validateorder() {
    return true;
}
// o/p: 12345

Enhancing Asynchronous Operations with Promise Chaining

A more efficient method for managing several asynchronous task sequentially is made possible by promise chaining. The resolved value from the previous promise is passed to each .then block, allowing data or actions to flow smoothly.

Promise Chaining :

Promise chaining improves the readability and maintainability of code by using the output of one promise as the input for the next operation.

createOrder(cart)
  .then(function (orderId) {
    // Process the order and return data for chaining
    return proceedToPayment(orderId);
  })
  .then(function (paymentInfo) {
    // Handle payment information
    console.log(paymentInfo);
  })
  .catch(function (err) {
    // Catch any errors during promise execution
    console.log(err);
  })

Managing Errors Truly

A crucial component of promise-based workflows is error handling. We can ensure graceful error management by using .catch to capture any rejections that happen during promise execution.

.catch Error Handling

We may centralise error handling by using the.catch block, which offers a fallback for any promise chain rejections that go unhandled.

createOrder(cart)
  .then(function (orderId) {
    // Process the order and return data for chaining
    return proceedToPayment(orderId);
  })
  .catch(function (err) {
    // Handle errors gracefully
    console.log(err);
  });
// we cannot call resolve twice(i.e promises are resolved once only).

Few key points to understand the topic more efficiently are:

1. The new Promise() constructor method can be used to generate a Promise.
2. A callback function is an argument passed to this constructor function.
3. "Resolve" and "reject" are the two arguments passed to the callback function. JS provides the keywords resolve and reject.
4. Our only option is to resolve or reject a promise. There is nothing more that can be done.
5. You can also use new Error('error message') to produce an error.
6. Another option is to attach a failure callback method, or .catch(), to handle any errors that may arise while the promise chain is being executed.

7. Only .then() errors that are present above it are handled by .catch. Should there be a .then() function behind it, catch will not address any errors related to it, and that .then will always be run.
8. In certain cases, it can be helpful if we wish to identify errors for a certain chain link.
9. Depending on the requirements, we can have numerous catches, with a general catch coming in the end.
10. Never forget to use the promise chain to return a value for the next .then.

Conclusion

Developing reliable and effective JavaScript apps requires a solid understanding of promise formation, chaining, and error management. Developers can improve code stability and speed asynchronous operations by using these concepts and best practices.

Read my previous blog part 19 to get better understanding of promises, before this blog....