Summary

We’ve seen that it’s possible, and relatively simple, to make HTML5 apps work in old browsers by performing feature detection (as by design, most—but sadly not all—HTML5 features can be programmatically detected) and patching in support with helper script. However, it’s important to be aware that polyfills probably won’t perform as well as their native counterparts, and that older browsers like IE6 will be further slowed down by their non-performing JavaScript engines. It may well be better in these cases to avoid polyfilling and provide a completely different fallback solution.