Handling asynchronous operations in JavaScript is essential for creating efficient and fluid applications. This is where promises come into play. Have you ever wondered how to keep your code from blocking while waiting for a response from a server? Or perhaps, how can you execute certain tasks only after another has finished? Well, promises in JavaScript are the solution you were looking for.

In this article, we'll explore what promises are, how they work, and how they can improve the flow of your app. Let's dive into the details.

What is a Promise in JavaScript?

A promise in JavaScript is an object that represents the eventual completion (or failure) of an asynchronous operation and its resulting value. In other words, a promise is an intermediary that handles asynchronous code execution and allows you to work with values ​​that are not yet known at the time of writing the code.

Key features of promises:

• Pending: The initial state, where the asynchronous operation has not yet finished.
• Resolved (Fulfilled): The asynchronous operation has completed successfully and a result has been obtained.
• Rejected: The asynchronous operation failed and a reason or error is provided.

This life cycle of a promise allows asynchronous operations to be handled more clearly and efficiently, avoiding the "callback hell".

Why Use Promises?

Promises are particularly useful when working with requests to servers. Imagine that you make an HTTP request to obtain data. The wait time can vary, and you don't want your application to freeze while the response arrives. Using promises allows your code to continue executing without waiting, which improves the overall performance of your application.

In addition, promises are applicable in other cases, such as:

• File manipulation: You can wait for a file to be uploaded or processed before running another task.
• DOM Modifications: If you need to ensure that certain interface changes are complete before continuing with other operations.

Promises also allow you to chain together multiple asynchronous operations in a more readable and maintainable way.

How to Use Promises in JavaScript

To create a promise, the Promise constructor is used, passing a function with two arguments: resolve and reject.

let miPromesa = new Promise((resolve, reject) => {
    // Simulación de una operación asíncrona
    let exito = true;

    if (exito) {
        resolve("Operación exitosa!");
    } else {
        reject("Ocurrió un error.");
    }
});

To handle the result of a promise, the .then() and .catch() methods are used:

miPromesa
    .then((mensaje) => {
        console.log(mensaje); // "Operación exitosa!"
    })
    .catch((error) => {
        console.error(error); // "Ocurrió un error."
    });`

Advantages of Promises over Callbacks

Before promises were introduced, handling asynchronous operations was primarily done with callbacks. However, this could lead to code that was difficult to follow and maintain, especially when multiple callbacks were nested, known as "callback hell".

Advantages of promises:

• Readability: The code is easier to read and follow.
• Maintenance: Facilitates the identification and handling of errors.
• Chaining: You can chain multiple asynchronous operations in a more organized way.

Promises vs Async/Await

Although promises have been a significant improvement over callbacks, the introduction of async/await in ECMAScript 2017 has further simplified the syntax for handling asynchronous operations.

async function obtenerDatos() {
    try {
        let response = await fetch('https://jsonplaceholder.typicode.com/posts/1');
        let data = await response.json();
        console.log(data);
    } catch (error) {
        console.error('Error:', error);
    }
}

With async/await, the code becomes more linear, similar to synchronous code, but is still asynchronous under the hood. However, it is important to note that async/await still uses promises at its core, so understanding how promises work is key to mastering the use of async/await.

Conclusion

Promises in JavaScript are a powerful tool for handling asynchronous operations without complicating your code with multiple callbacks. From requests to servers to more complex tasks within your application, promises allow you to write cleaner, more readable, and easier to maintain code.

No matter if you are building a simple web application or a more complex system, learning how to handle promises is essential to optimize the performance of your code.