Polyfills are scripts that provide modern functionality on older browsers that do not support certain features of JavaScript. They essentially "fill in" the gaps, allowing developers to use newer web standards without worrying about compatibility issues.

Commonly Used Polyfills in JavaScript

Here are some popular polyfills:

• Promise: Adds support for the Promise API, which allows for asynchronous programming.
• Fetch: Provides a modern way to make network requests, replacing older XMLHttpRequest.
• Array.prototype.includes: Adds the includes method to arrays, allowing for easier checks for the presence of an element.
• Object.assign: Enables the merging of objects, which is useful for cloning or extending objects.
• String.prototype.startsWith: Adds a method to check if a string starts with a specified substring.

Using polyfills helps ensure that your web applications work smoothly across different browsers, enhancing user experience.