Progressive Enhancement
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Publishing a draft originally written in 2015, Remy shows Progressive Enhancement is still a strong topic all developers should understand and work on:
Developers are inherently lazy. It's what makes them/us optimise our workflows and become very good at solving problems. We re-use what's known to work and tend to eke out the complex parts that we can "live without". Sadly, this can be at the cost of accessibility and progressive enhancement.
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Since JavaScript doesn't exhibit the same resilience that HTML & CSS does, so the fear is that it'll leave users who can't upgrade, faced with a broken or blank page.