What are Promises in React.js?

In React, there are various ways to work with asynchronous data, but using Promises is one of the most popular ones. A Promise is an object that represents an asynchronous operation. It stands for a value that will be resolved in the future, in other words.

In this post, we'll examine the significance of promises, their underlying API, and some common pitfalls to watch out for while utilizing them. We'll also give a simple illustration of how to manage asynchronous programming using promises.

You will know more about using Promises in React.js at the conclusion of this post and be able to apply them to your own projects.

So without further ado, let's get started!

Promises in React.js

Like promises in other programming languages, React promises work similarly. An object that depicts the outcome of an asynchronous operation is called a promise which helps in managing asynchronous actions like data fetching. Working with Promises is simple with React because of its integrated Promise API.

A promise is in a pending condition when it is created. This indicates that the async procedure is still ongoing. Depending on the outcome of the async operation, the promise will either be fulfilled or denied. Upon successful completion of the async procedure, the promise will be fulfilled. The promise will be turned down if the async procedure fails.

By using promises, we can see which functions are interdependent, making the code easier to comprehend and debug without having to go through a long list of nested function calls.

How does Promises work in React.js?

React has a built-in way of working with Promises called the Promises rendering model. This model allows you to work with async data in a declarative way. In this model, you only need to worry about three things −

  • The loading state: This is when data is being fetched from the async operation.

  • The error state: This is when there was an error fetching the data.

  • The data itself: This is the resolved value from the async operation.

This may seem like a lot, but Promises make it easy to handle all of these states without getting bogged down in details.

When we make a request, we do not always know when the response will come back. With Promises, we can write code that will wait for the response to come back, and then do something with the data.

What Do promises usually look like in JavaScript? See this example -

function doSomething() { var promise = new Promise(function(resolve, reject) { setTimeout(function() { resolve('Success!'); // Yay! Everything went well! }, 2000); }); return promise; // This is what we'll use later. Promise that something will happen!}

We give a "executor function"—a function that will be called in the future when the Promise is called—when we create a promise. Resolve and Reject are the two parameters for the executor function. The Promise can be resolved using the resolve function and rejected using the reject function.

The following example shows how to use a Promise with .then and .catch in React -

doSomething().then( function(result) { console.log(”The function executed successfully!”) }).catch

When the promise is resolved, the .then() method runs and the Promise's outcome is passed on to it (which is the data that was loaded from the external source), thereafter runs whatever function is inside the then() method.

If the promise fails, then the .catch() method runs which catches the error and is often used in React.js for error handling.

Different Ways to use Promises

There are a few different ways to use Promises in React.js like with fetch() and async/await. Both of these methods have the same goal - to make working with asynchronous code simpler and more efficient.

One of the most common ways to use Promises is to load data from an API, and this is where we make use of async and await.

When you make an API call, you usually have to wait for the server to respond before you can do anything with the data. This can lead to issues if you're not careful, but with Promises you can avoid these problems by waiting for the API call to finish before you try to use the data.

Another way you can use Promises is to handle errors. When you make an API call, there's always a chance that it might fail, in that case, you can always use the .catch() method to handle the errors.

Why use Promises?

In short, they make dealing with asynchronous code in JavaScript much easier.

Async data is data that is not available immediately. It can take a little bit of time to load. When working with asynchronous data in React, there are often times when you need to wait for a certain condition to be met before you can continue.

This is where Promises come in. Promises are a great way to handle asynchronous operations in React.js, and they can help you create more responsive and scalable applications. With Promises, you can avoid the callback hell that can often occur when working with asynchronous code.

There are a few benefits of using Promises in React.js -

  • Manage asynchronous code in a more efficient and organized way.

  • Avoid "callback hell" and keep your code clean and readable. Promises can also be chained together, so you can easily create complex asynchronous interactions.

  • Help you load data from multiple sources in parallel and they can make it easier to cancel async requests.


In conclusion, promises play an important role in React applications. They can help you make your code more readable and easier to debug. Promises also give you greater control over how your application handles asynchronous code.