Shim and Polyfill

Shims and polyfills are both tools web developers use to address compatibility issues across different browsers. Here's a breakdown of how they differ:

Polyfill

• A more specific type of shim.
• Focuses on providing a complete implementation of a missing API (Application Programming Interface) for older browsers.
• Essentially acts like a replacement for the missing functionality.
• Often used to enable modern features like fetch or Promise in legacy browsers.

Shim

• A broader term for any code that acts as an adapter between different systems.
• Can be used for various purposes, including:
  1. Providing a new API to an older environment (similar to a polyfill).
  2. Correcting the behavior of existing code.
  3. Interacting with different libraries or frameworks.
• May not provide a complete implementation, but rather adjust behavior or bridge gaps.

Analogy

• Think of a polyfill as a complete replica of a furniture piece (e.g., a modern chair) that you can use in place of a missing one in an older set.
• A shim would be more like an adapter that allows you to use a chair from a different set (e.g., a vintage chair) with your modern table. It might not be a perfect match, but it makes things work together.

In essence

• All polyfills are shims, but not all shims are polyfills.
• Polyfills are specifically designed for browser compatibility and filling in missing APIs.