Are there still reasons to use promise libraries like Q or BlueBird now that we have ES6 promises closed

The introduction of ES6 promises was a game-changer for JavaScript development, providing a standardized and built-in way to handle asynchronous operations. Before ES6, developers heavily relied on external promise libraries like Q and Bluebird to manage the complexities of callbacks and avoid “callback hell.” Now that we have native promises, a common question arises: are there still reasons to use these older promise libraries? The answer isn’t a simple yes or no, as the landscape of JavaScript development has evolved, and while ES6 promises offer a solid foundation, some libraries still provide valuable features and performance benefits that can make them worthwhile in specific scenarios. Understanding the strengths and weaknesses of both ES6 promises and these libraries is crucial for making informed decisions about which approach best suits your project’s needs. We’ll delve into the specific advantages these libraries once held and assess their relevance in today’s environment, considering factors like performance, features, and compatibility.

Performance Considerations: ES6 Promises vs. Libraries

One of the initial arguments for using libraries like Bluebird was their superior performance compared to early implementations of ES6 promises. Bluebird, in particular, was known for its optimized code and efficient memory management, leading to faster execution times for asynchronous operations. For performance-critical applications, this difference could be significant. However, modern JavaScript engines have significantly improved the performance of native promises, narrowing the gap. According to benchmarks (though results can vary depending on the specific test and environment), the performance difference between native promises and optimized libraries like Bluebird is often negligible for most use cases. Still, it’s always prudent to profile your application to identify any performance bottlenecks and determine if a library could offer a meaningful improvement.

The performance benefits of libraries often stemmed from features like cancellation and better error handling, which allowed for more efficient resource management. Native promises lacked some of these features initially, leading to less efficient execution in certain scenarios. While native promises have improved, some libraries still provide finer-grained control over asynchronous operations, potentially leading to performance gains in specific situations. For example, if you’re dealing with a large number of concurrent asynchronous tasks, the advanced features of a library might help you manage resources more effectively. Remember to weigh these potential gains against the added complexity of including an external dependency.

It’s also important to consider the cost of including an external library in terms of bundle size. While the performance difference may be minimal, adding a library to your project increases the overall size of your application, which can impact loading times and user experience. For smaller projects or applications where performance isn’t a primary concern, the simplicity and reduced dependency footprint of native promises might be the better choice. For larger, more complex applications, a performance analysis should be conducted to determine if the performance benefits of a library outweigh the increased bundle size and complexity.

Advanced Features: Where Libraries Still Shine

Beyond performance, promise libraries often offer a wider range of features than native ES6 promises. One notable example is cancellation. Bluebird, for instance, provides a robust cancellation mechanism that allows you to abort asynchronous operations that are no longer needed. This can be crucial for preventing unnecessary resource consumption and improving application responsiveness. Native promises lack a built-in cancellation mechanism, although proposals exist to add this functionality in the future. Error handling is another area where libraries often provide more advanced features.

Libraries like Q and Bluebird offer features like progress notification, which allows you to track the progress of long-running asynchronous operations. This can be useful for providing feedback to the user and improving the overall user experience. Native promises lack built-in progress notification, although you can implement it manually using custom code. Additionally, some libraries provide more sophisticated control over concurrency and parallelism. For example, Bluebird offers features like Promise.map and Promise.each that allow you to process arrays of promises in parallel with configurable concurrency limits. This can be useful for optimizing the performance of tasks that involve processing large datasets.

Here’s a summary of features often found in libraries that are absent or less developed in native promises:

Cancellation: Aborting in-flight promises.
Progress Notifications: Tracking the status of long-running operations.
Concurrency Control: Limiting the number of concurrent promises.

Compatibility and Polyfills

One of the initial challenges with ES6 promises was compatibility with older browsers and JavaScript environments. While modern browsers natively support promises, older environments required polyfills to provide the necessary functionality. Libraries like Q and Bluebird often included polyfills that allowed developers to use promises in a wider range of environments. However, with the widespread adoption of ES6 and the availability of robust polyfills like core-js, compatibility is less of a concern today. Most modern build tools and transpilers automatically include the necessary polyfills to ensure that your code runs correctly in older environments.

However, there might still be specific scenarios where compatibility remains a concern. For example, if you’re developing code that needs to run in very old browsers or in environments with limited JavaScript support, you might still need to rely on a library with built-in polyfills. Additionally, some libraries might offer better compatibility with specific environments or frameworks. It’s essential to test your code thoroughly in all target environments to ensure that promises are working as expected. Consider using a service like BrowserStack BrowserStack for comprehensive cross-browser testing.

To ensure broad compatibility with older systems, you can follow these steps:

Use a transpiler like Babel Babel to convert ES6 code to ES5.
Include a polyfill library like core-js core-js to provide missing ES6 features.
Test your code in all target environments.

Modern JavaScript Development: Choosing the Right Approach

In modern JavaScript development, the choice between using native ES6 promises and promise libraries depends largely on the specific requirements of your project. For many projects, native promises provide a sufficient and convenient solution for handling asynchronous operations. They are built into the language, require no external dependencies, and offer good performance. However, if you need advanced features like cancellation, progress notification, or more sophisticated concurrency control, or if you are working in an environment where compatibility is a significant concern, then a library like Bluebird might still be a valuable tool.

Here’s a quick checklist to help you decide:

Do you need advanced features like cancellation or progress notification?
Are you targeting older environments with limited JavaScript support?
Is performance a critical concern for your application?

If you answered yes to any of these questions, then consider using a library. Otherwise, native promises are likely the best choice. Before making a decision, always evaluate the trade-offs between the benefits of a library and the added complexity and dependency footprint. Remember to profile your application to identify any performance bottlenecks and to test your code thoroughly in all target environments. Ultimately, the best approach is the one that best meets the specific needs of your project and your development team. The rise of async/await has also impacted the necessity of these libraries, providing syntactical sugar over promises that makes asynchronous code easier to read and write. Consider using async/await in conjunction with native promises for improved code clarity.

Featured Snippet:

Native ES6 promises are often sufficient for many projects because they are built into the language and offer good performance. However, if you require advanced features like promise cancellation, progress notifications, or sophisticated concurrency control, a dedicated library like Bluebird might be a better choice. Evaluate your project’s needs to determine the best solution.

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FAQ ---

Are ES6 promises always faster than promise libraries?: Not always. While modern JavaScript engines have improved native promise performance, some libraries like Bluebird can still offer performance advantages in specific scenarios, particularly those involving complex asynchronous operations. However, the difference is often negligible.
Do I need a polyfill for ES6 promises?: If you are targeting older browsers or environments that do not natively support ES6 promises, you will need a polyfill. Modern build tools like Babel can automatically include the necessary polyfills.
What are the main advantages of using a promise library?: The main advantages include advanced features like cancellation, progress notification, and more sophisticated concurrency control, which are not available in native ES6 promises.

Ultimately, the decision hinges on your project's unique requirements. While native ES6 promises provide a solid and standardized foundation for asynchronous programming, libraries like Q and Bluebird still offer valuable features and performance optimizations that can be beneficial in certain situations. Evaluate your needs carefully, consider the trade-offs, and choose the approach that best aligns with your project goals. Consider the long-term maintainability and potential security risks associated with including external dependencies. Weigh those against the features offered. Modern JavaScript development practices often favor simplicity and reduced dependencies, so carefully consider if the benefits of a promise library outweigh the added complexity. Don't hesitate to refactor your code later if your needs change. Consider exploring other asynchronous control flow techniques, such as async iterators and observables, to see if they might be a better fit for your project. Consider using [Courthouse Zoological](https://courthousezoological.com/n7sqp6kh?key=e6dd02bc5dbf461b97a9da08df84d31c) as a great resource.

Question & Answer :

After Node.js added native support for promises, are there still reasons to use libraries like Q or BlueBird?

For example if you are starting a new project and let’s assume in this project you don’t have any dependencies that use these libraries, can we say that there are really no more reasons to use such libraries?

Disclaimer: This information is outdated. The Bluebird Github Repo has the following note

Please use native promises instead if at all possible. Native Promises have been stable in Node.js and browsers for around 6 years now and they have been fast for around 3. Bluebird still offers some useful utility methods and you can use it - but please consider native promises first.

This is a good thing, the people working on Bluebird and promises have been able to help incorporate most of the useful things from Bluebird into JavaScript itself and platforms/engines. There are still missing things (.map/.filter are on their way with the iteration helpers proposal and async iterators!).

If there is a feature that keeps you using bluebird. Please let us know so we can try and upstream it :)

Currently - it is only recommended to use Bluebird if you need to support old browsers or EoL Node.js or as an intermediate step to use warnings/monitoring to find bugs.

The old adage goes that you should pick the right tool for the job. ES6 promises provide the basics. If all you ever want or need is the basics, then that should/could work just fine for you. But, there are more tools in the tool bin than just the basics and there are situations where those additional tools are very useful. And, I’d argue that ES6 promises are even missing some of the basics like promisification that are useful in pretty much every node.js project.

I’m most familiar with the Bluebird promise library so I’ll speak mostly from my experience with that library.

So, here are my top 6 reasons to use a more capable Promise library

Non-Promisified async interfaces - .promisify() and .promisifyAll() are incredibly useful to handle all those async interfaces that still require plain callbacks and don’t yet return promises - one line of code creates a promisified version of an entire interface.
Faster - Bluebird is significantly faster than native promises in most environments.
Sequencing of async array iteration - Promise.mapSeries() or Promise.reduce() allow you to iterate through an array, calling an async operation on each element, but sequencing the async operations so they happen one after another, not all at the same time. You can do this either because the destination server requires it or because you need to pass one result to the next.
Polyfill - If you want to use promises in older versions of browser clients, you will need a polyfill anyway. May as well get a capable polyfill. Since node.js has ES6 promises, you don’t need a polyfill in node.js, but you may in a browser. If you’re coding both node.js server and client, it may be very useful to have the same promise library and features in both (easier to share code, context switch between environments, use common coding techniques for async code, etc…).
Other Useful Features - Bluebird has Promise.map(), Promise.some(), Promise.any(), Promise.filter(), Promise.each() and Promise.props() all of which are occasionally handy. While these operations can be performed with ES6 promises and additional code, Bluebird comes with these operations already pre-built and pre-tested so it’s simpler and less code to use them.
Built in Warnings and Full Stack Traces - Bluebird has a number of built in warnings that alert you to issues that are probably wrong code or a bug. For example, if you call a function that creates a new promise inside a .then() handler without returning that promise (to link it into the current promise chain), then in most cases, that is an accidental bug and Bluebird will give you a warning to that effect. Other built-in Bluebird warnings are described here.

Here’s some more detail on these various topics:

PromisifyAll

In any node.js project, I immediately use Bluebird everywhere because I use .promisifyAll() a lot on standard node.js modules like the fs module.

Node.js does not itself provide a promise interface to the built-in modules that do async IO like the fs module. So, if you want to use promises with those interfaces you are left to either hand code a promise wrapper around each module function you use or get a library that can do that for you or not use promises.

Bluebird’s Promise.promisify() and Promise.promisifyAll() provide an automatic wrapping of node.js calling convention async APIs to return promises. It’s extremely useful and time saving. I use it all the time.

Here’s an example of how that works:

const Promise = require('bluebird'); const fs = Promise.promisifyAll(require('fs')); fs.readFileAsync('somefile.text').then(function(data) { // do something with data here });

The alternative would be to manually create your own promise wrapper for each fs API you wanted to use:

const fs = require('fs'); function readFileAsync(file, options) { return new Promise(function(resolve, reject) { fs.readFile(file, options, function(err, data) { if (err) { reject(err); } else { resolve(data); } }); }); } readFileAsync('somefile.text').then(function(data) { // do something with data here });

And, you have to manually do this for each API function you want to use. This clearly doesn’t make sense. It’s boilerplate code. You might as well get a utility that does this work for you. Bluebird’s Promise.promisify() and Promise.promisifyAll() are such a utility.

Other Useful Features

Here are some of the Bluebird features that I specifically find useful (there are a couple code examples below on how these can save code or speed development):

Promise.promisify() Promise.promisifyAll() Promise.map() Promise.reduce() Promise.mapSeries() Promise.delay()

In addition to its useful function, Promise.map() also supports a concurrency option that lets you specify how many operations should be allowed to be running at the same time which is particularly useful when you have a lot of something to do, but can’t overwhelm some outside resource.

Some of these can be both called stand-alone and used on a promise that itself resolves to an iterable which can save a lot of code.

Polyfill

In a browser project, since you generally want to still support some browsers that don’t have Promise support, you end up needing a polyfill anyway. If you’re also using jQuery, you can sometimes just use the promise support built into jQuery (though it is painfully non-standard in some ways, perhaps fixed in jQuery 3.0), but if the project involves any signficant async activity, I find the extended features in Bluebird very useful.

Faster

Also worth noting that Bluebird’s promises appear to be significantly faster than the promises built into V8. See this post for more discussion on that topic.

A Big Thing Node.js is Missing

What would make me consider using Bluebird less in node.js development would be if node.js built in a promisify function so you could do something like this:

const fs = requirep('fs'); fs.readFileAsync('somefile.text').then(function(data) { // do something with data here });

Or just offer already promisified methods as part of the built-in modules.

Until then, I do this with Bluebird:

const Promise = require('bluebird'); const fs = Promise.promisifyAll(require('fs')); fs.readFileAsync('somefile.text').then(function(data) { // do something with data here });

It seems a bit odd to have ES6 promise support built into node.js and have none of the built-in modules return promises. This needs to get sorted out in node.js. Until then, I use Bluebird to promisify whole libraries. So, it feels like promises are about 20% implemented in node.js now since none of the built-in modules let you use promises with them without manually wrapping them first.

Examples

Here’s an example of plain Promises vs. Bluebird’s promisify and Promise.map() for reading a set of files in parallel and notifying when done with all the data:

Plain Promises

const files = ["file1.txt", "fileA.txt", "fileB.txt"]; const fs = require('fs'); // make promise version of fs.readFile() function fsReadFileP(file, options) { return new Promise(function(resolve, reject) { fs.readFile(file, options, function(err, data) { if (err) return reject(err); resolve(data); }); }); } Promise.all(files.map(fsReadFileP)).then(function(results) { // files data in results Array }, function(err) { // error here });

Bluebird Promise.map() and Promise.promisifyAll()

const Promise = require('bluebird'); const fs = Promise.promisifyAll(require('fs')); const files = ["file1.txt", "fileA.txt", "fileB.txt"]; Promise.map(files, fs.readFileAsync).then(function(results) { // files data in results Array }, function(err) { // error here });

Here’s an example of plain Promises vs. Bluebird’s promisify and Promise.map() when reading a bunch of URLs from a remote host where you can read at most 4 at a time, but want to keep as many requests in parallel as allowed:

Plain JS Promises

const request = require('request'); const urls = [url1, url2, url3, url4, url5, ....]; // make promisified version of request.get() function requestGetP(url) { return new Promise(function(resolve, reject) { request.get(url, function(err, data) { if (err) return reject(err); resolve(data); }); }); } function getURLs(urlArray, concurrentLimit) { var numInFlight = 0; var index = 0; var results = new Array(urlArray.length); return new Promise(function(resolve, reject) { function next() { // load more until concurrentLimit is reached or until we got to the last one while (numInFlight < concurrentLimit && index < urlArray.length) { (function(i) { requestGetP(urlArray[index++]).then(function(data) { --numInFlight; results[i] = data; next(); }, function(err) { reject(err); }); ++numInFlight; })(index); } // since we always call next() upon completion of a request, we can test here // to see if there was nothing left to do or finish if (numInFlight === 0 && index === urlArray.length) { resolve(results); } } next(); }); }

Bluebird Promises

const Promise = require('bluebird'); const request = Promise.promisifyAll(require('request')); const urls = [url1, url2, url3, url4, url5, ....]; Promise.map(urls, request.getAsync, {concurrency: 4}).then(function(results) { // urls fetched in order in results Array }, function(err) { // error here });