Chapter 7. Building Your First Prollyfill

In Chapters 3 through 5, I walked you through the exercise of building a polyfill for the HTML5 Forms spec. Over the course of those three chapters, we talked about how to make a plan for building a polyfill, how to go about initial development, how to configure your library for automated and cross-browser testing, and finally, how to build your polyfill for performance.

In Chapter 6, I introduced the concept of the prollyfill and walked through several examples of popular prollyfilling libraries. In this chapter, we’re going to build on that knowledge, along with what we learned earlier in the book, and build our own prollyfill to test out an experimental web platform feature. Along the way, you’ll learn the ways that building polyfills and prollyfills are similar, and the ways they differ.

Prollyfills vs. Polyfills: What’s the Difference?

Prollyfills, as we discussed in Chapter 6, are quite similar to polyfills in many ways, the biggest difference being that they often target proposals or specifications with in-flux APIs. Sometimes they even target untested or unspecified ideas altogether. In both cases, much of the ideas that surround the prollyfill, including the API, are expected to change greatly as the idea is debated, tested, and possibly accepted for standardization.

In addition, the purpose of building a prollyfill differs from that of a polyfill. Polyfills are typically built to allow developers to rely on new features and ...

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