Polyfill – Definition and meaning

What is a polyfill?

A polyfill is a piece of code (usually JavaScript) that makes it possible to use modern web technologies in older browsers that do not natively support these functions. Polyfills extend the JavaScript object to emulate features that are available in newer versions of JavaScript or in certain APIs.

Why is a polyfill important?

Polyfills are crucial for web development because they ensure greater compatibility between different browsers and their versions. They allow developers to utilise modern features without worrying incompatibilities, improving the user experience.

Examples of commonly used polyfills

• Promise Polyfill: For supporting Promises in older browsers that do not support this feature.
• Fetch Polyfill: Enables the use of the Fetch API to make HTTP requests.
• Array.from Polyfill: Allows the conversion of array-like objects into real arrays.

How a polyfill works

A polyfill first checks whether the browser already supports the functionality. If not, the polyfill is executed to provide the required functionality. Here is a simple example:

// Polyfill for the Array.prototype.includes method if (!Array.prototype.includes) { Array.prototype.includes = function(value) { return this.indexOf(value) !== -1; }; }

When should you use polyfills?

Using polyfills makes sense if:

• You want to use modern web technologies but want to ensure your website works in older browsers.
• Your target audience uses a wide range of browsers.
• The usability of your application or website should not be impaired.

Polyfills vs. shims

It is important to distinguish polyfills from shims. While polyfills provide native support for new features, shims are a piece of code that adds functionality after the fact or modifies existing functionality to work better in older browsers. For example, a shim can be used to create a completely new function that does not exist in older browsers. Polyfills, on the other hand, try to mimic the native behaviour.

Challenges of using polyfills

Although polyfills offer many advantages, there are also some challenges:

• Performance: polyfills can affect the performance of an application or website, especially if they are not optimised.
• Maintainability: Overuse of polyfills can clutter code and make it difficult to maintain.

Conclusion

Polyfills are an important tool in a web developer's armoury. They ensure that modern applications remain accessible on as many devices and browsers as possible. However, if you decide to use polyfills, you should carefully consider which functions are really necessary and what impact they may have on the performance of your application.

Illustrative example on the topic: Polyfill

Imagine you are developing a new web application that uses the Array.prototype.includes function to check whether certain values are present in an array. You want the application to work in both modern and older browsers, such as Internet Explorer 11. Without a polyfill, the functionality would not be available in IE 11, which would result in many users encountering difficulties or not being able to use the application properly. By using a polyfill that replicates the includes method, you ensure that your application works well for all users, regardless of their browser version. In this way, you not only improve the accessibility, but also the user experience of your application.

For more information on relevant topics, you can also explore the terms JavaScript and Feature Detection.