I Built a Retro NES Emulator in Hours- Something That Used to Take Months

A browser-based NES emulator with PS4 controller support, full-screen scaling, and real audio - built in a single afternoon. Here's what vibe coding actually looks like when you push it on something real.

Not long ago, building something like a browser-based NES emulator would have been a serious undertaking reserved for developers with years of experience under their belt.

We're talking deep JavaScript knowledge, an understanding of rendering pipelines, audio synchronization, controller input systems, and a working mental model of how emulator architecture actually functions. This wasn't a weekend project. This was the kind of thing you'd see on a developer's GitHub with a long commit history, a detailed README, and a story that started with "I spent six months on this."

For most people, that story ended before it began.

A Bit of Personal Background

I've been a digital marketer for 18 years. I'm not a developer by trade, but I've always had a builder mentality - I write code when it serves a purpose, and I've shipped HTML tools, automation workflows, and client-facing dashboards along the way.

One of the things that fell off as life got busier was gaming. Specifically, the kind of gaming I grew up on: the original Nintendo. There's a particular joy to those 8-bit games that modern titles, as impressive as they are, don't quite replicate. I'd thought about building a browser-based emulator for years — something I could open on any machine, drop in a ROM, and be playing within seconds.

The problem was that building one properly always felt just out of reach. Not impossible. Just expensive in terms of time I didn't have. Then I tried vibe coding.

What "Vibe Coding" Actually Means

If you haven't heard the term, vibe coding is the practice of building software through natural language conversation with an AI - describing what you want, iterating on the output, debugging collaboratively, and shipping something real without necessarily writing every line yourself.

It doesn't mean you're completely hands-off. You're still making every decision about what gets built, how it behaves, and what the experience feels like. But you're no longer the bottleneck. The friction between "I have an idea" and "I have a working thing" collapses dramatically. That's the shift worth paying attention to.

The friction between "I have an idea" and "I have a working thing" collapses dramatically.

What I Actually Built

https://video.wixstatic.com/video/9100d2_d1218974a5a24bfa9a0d6e873fefbdb1/720p/mp4/file.mp4

In a single working session, I put together a fully functional, browser-based NES emulator. Here's what it includes:

The Technology Behind It

Even though AI accelerated the build, the technology underneath is entirely real. Here is what makes up the stack

The emulator core itself is JSNES — an open-source JavaScript NES emulation library that handles the actual CPU, PPU, and APU emulation. I didn't write that from scratch, and I don't pretend otherwise. What I built is the integration layer: the UI, the controls, the audio pipeline, the rendering loop, and the overall experience. That distinction matters, and I'll come back to it.

The Time Comparison That Changes Everything

The gap between those two timelines is not a minor efficiency gain. It's a different category of experience entirely.

What the Debugging Actually Looked Like

This is the part most vibe coding articles gloss over, so I want to be honest about it.

The first version had color problems. The frame buffer from JSNES stores pixel data in a specific byte order — red in the lowest byte, green in the middle, blue above that — and getting the Canvas API's ImageData to display it correctly required understanding what was actually going wrong, not just asking the AI to "fix the colors."

There was also audio stutter on lower-end hardware. The Web Audio API's ScriptProcessor buffers audio samples, but if the buffer fills up faster than it drains, you get latency. If it empties too fast, you get silence or crackle. The fix involved capping the buffer length at 16,384 samples and splicing the overflow — a specific, technical decision that required understanding the problem before being able to describe it clearly enough to solve it.

The fullscreen scaling was its own challenge. NES games render at 256x240, a non-standard aspect ratio. Getting that to fill a modern widescreen monitor without distortion meant using CSS min() functions to calculate the largest size that fits within both axes simultaneously. It's elegant once it's working. It took iteration to get right.

None of this happened automatically. I had to identify what was broken, understand why, and direct the process. The AI was a highly capable collaborator — not an autonomous builder.

What AI Doesn't Replace

AI didn't decide what features to build. It didn't notice that the audio was stuttering. It didn't realize that fullscreen mode was distorting the aspect ratio. It didn't prioritize PS4 controller support over other possible improvements.

Every one of those decisions came from me. What changed is how quickly I could act on that judgment.

This is actually closer to how experienced engineers work than most people realize. Senior developers don't write everything from scratch either. They know which libraries to pull in, how to evaluate tradeoffs, and how to integrate components into something coherent. They've done it enough times that the implementation details are almost automatic - their mental energy goes to decisions, not syntax. AI just made that mode of working accessible to more people.

Five Things This Experience Reinforced

1. You Don't Need to Master Everything Before You Start

The barrier to beginning used to be the entire learning curve. Now it's just the first prompt. You can build real, functional tools while you're still learning — and the building accelerates the learning.

2. AI Turns Coding Into Assembly and Decision-Making

Less time typing boilerplate. More time thinking about what the thing should do and how it should feel to use. For anyone with strong product instincts and weak implementation bandwidth, this is a meaningful unlock.

3. Speed Is a Competitive Advantage

If you can build a working prototype in an afternoon instead of a month, you can test ideas faster, get feedback sooner, and iterate more aggressively. In a market where attention is scarce, the ability to show rather than describe is increasingly valuable.

4. Learning Still Matters - It Just Happens Differently

The goal isn't to skip understanding. It's to engage with understanding at the moment it becomes relevant. Debugging a real audio pipeline teaches you more about the Web Audio API than a tutorial ever would.

5. The Floor Dropped. The Ceiling Didn't.

What used to take months now takes hours — that's the entry-level story. But the ceiling for what you can build is still determined by how much taste, judgment, and domain knowledge you bring to the process.

The question is no longer "Can I build this?" It's now: "How fast can I get this working?"

Thank you Claude for bringing back happy gaming memories!

By the way, if you want a copy of the NES Emulator and a couple of old school NES roms, just send a DM. I'll send you copy. Enjoy!