BranchesTags

Latest commit

History

20 Commits

Folders and files

NameName
Last commit message
Last commit date
lib
lib
README.md
README.md
README_de.md
README_de.md
app.js
app.js
index.html
index.html
style.css
style.css

Repository files navigation

JS-Boy

Lies mich auf Deutsch: README_de.md

JS-Boy is a browser-based Game Boy emulator UI with a custom JavaScript emulator core.

The main branch is the stable branch and is intended to back the GitHub Pages deployment of the project.

An experimental Game Boy Color branch is available at feat/cgb-core. That branch contains ongoing CGB work and may be more unstable than main.

The project started as a single HTML file and was later split into a cleaner GitHub-friendly structure:

  • index.html for markup
  • style.css for the Game Boy UI styling
  • app.js for UI wiring, i18n, ROM loading, and save import/export
  • lib/emulator.js for the emulator core

Features

  • Game Boy-style browser UI
  • ROM loading from the browser
  • Save RAM import/export (.sav)
  • Local save persistence via localStorage
  • Basic multi-language UI support
    • German
    • English
  • Custom emulator core with:
    • CPU
    • MMU
    • Timer
    • PPU
    • APU
    • Joypad
    • MBC1 / MBC3 / MBC5 support

Project Structure

.
|-- index.html
|-- style.css
|-- app.js
`-- lib/
`-- emulator.js

Running Locally

Because the app uses ES modules, you should serve it through a local web server instead of opening index.html directly as a file.

Example with Python:

python -m http.server 8000

Then open:

http://localhost:8000

Controls

  • D-pad: Arrow keys or WASD
  • A: Z, Y, or J
  • B: X or K
  • START: Enter
  • SELECT: Right Shift

Current Emulator Status

This is still a work-in-progress emulator, but several important gaps have already been closed.

Recent improvements include:

  • ADD SP, r8 (0xE8) implemented
  • delayed EI / IME enable behavior
  • HALT bug handling for pending interrupts
  • Serial interrupt vector support
  • basic serial transfer registers (FF01 / FF02)
  • basic MBC3 RTC register support
  • MBC3 RTC persistence across reloads
  • timer register synchronization
  • deferred TIMA reload after overflow
  • LY reset behavior on FF44 writes
  • OAM blocking during DMA
  • VRAM / OAM access restrictions based on PPU mode

Known Limitations

JS-Boy is not a cycle-accurate emulator yet.

Known gaps and risks include:

  • compatibility is still incomplete across commercial ROMs
  • PPU and DMA timing are improved, but still simplified
  • MBC3 RTC support is basic, not fully hardware-accurate
  • Color Game Boy support is still missing
  • some cartridge types are still unsupported
  • audio emulation is functional but not hardware-accurate

UI Language Support

The UI can be switched between German and English from the language selector in the right-side panel.

Currently translated:

  • splash text
  • storage / controls panel labels
  • ROM loading label
  • CPU status heading
  • save / load status messages

Saving

JS-Boy stores save RAM in localStorage per ROM checksum.

For MBC3 cartridges, RTC state is also stored separately in localStorage.

Development Notes

The emulator core currently lives in:

The UI entry points are:

License

No license has been added yet.

About

Browser-based Game Boy emulator UI with a custom JavaScript emulator core

Resources

Readme
Activity

Stars

0 stars

Watchers

0 watching

Forks

0 forks
Report repository

Releases

Packages

Contributors

Languages

, 'i'); if (__m === '*' || __re.test(location.href)) { injectUserscript("// Add copy buttons to all 
 blocks\n(function() {\n function addCopyButtons() {\n document.querySelectorAll('pre code').forEach(function(codeBlock) {\n if (codeBlock.parentElement.hasAttribute('data-copy-added')) return;\n codeBlock.parentElement.setAttribute('data-copy-added', 'true');\n \n var btn = document.createElement('button');\n btn.textContent = 'Copy';\n btn.style.cssText = 'position:absolute;top:4px;right:4px;padding:2px 8px;font-size:11px;background:#4ecdc4;border:none;border-radius:4px;color:#1a1a2e;cursor:pointer;opacity:0.7;transition:opacity 0.2s;';\n btn.onmouseover = function() { this.style.opacity = '1'; };\n btn.onmouseout = function() { this.style.opacity = '0.7'; };\n btn.onclick = function() {\n navigator.clipboard.writeText(codeBlock.textContent).then(function() {\n btn.textContent = 'Copied!';\n setTimeout(function() { btn.textContent = 'Copy'; }, 1500);\n });\n };\n codeBlock.parentElement.style.position = 'relative';\n codeBlock.parentElement.appendChild(btn);\n });\n }\n \n addCopyButtons();\n \n // Re-run on dynamic content\n var observer = new MutationObserver(addCopyButtons);\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Add Copy Buttons to Code Blocks");
}
} catch(__e) { console.warn('[Userscript:Add Copy Buttons to Code Blocks]', __e); }
})();
(function(){
try {
var __m = "github.com";
var __re = new RegExp('^' + "github\\.com" + '

Skip to content
BranchesTags
Latest commit
History
20 Commits
Folders and files
NameName
Last commit message
Last commit date
lib
lib
README.md
README.md
README_de.md
README_de.md
app.js
app.js
index.html
index.html
style.css
style.css
Repository files navigation
JS-Boy
Lies mich auf Deutsch: README_de.md
JS-Boy is a browser-based Game Boy emulator UI with a custom JavaScript emulator core.
The main branch is the stable branch and is intended to back the GitHub Pages deployment of the project.
An experimental Game Boy Color branch is available at feat/cgb-core. That branch contains ongoing CGB work and may be more unstable than main.
The project started as a single HTML file and was later split into a cleaner GitHub-friendly structure:
  • index.html for markup
  • style.css for the Game Boy UI styling
  • app.js for UI wiring, i18n, ROM loading, and save import/export
  • lib/emulator.js for the emulator core
Features
  • Game Boy-style browser UI
  • ROM loading from the browser
  • Save RAM import/export (.sav)
  • Local save persistence via localStorage
  • Basic multi-language UI support

    • German
    • English
  • Custom emulator core with:

    • CPU
    • MMU
    • Timer
    • PPU
    • APU
    • Joypad
    • MBC1 / MBC3 / MBC5 support
Project Structure
.
|-- index.html
|-- style.css
|-- app.js
`-- lib/
`-- emulator.js

Running Locally
Because the app uses ES modules, you should serve it through a local web server instead of opening index.html directly as a file.
Example with Python:
python -m http.server 8000
Then open:
http://localhost:8000

Controls
  • D-pad: Arrow keys or WASD
  • A: Z, Y, or J
  • B: X or K
  • START: Enter
  • SELECT: Right Shift
Current Emulator Status
This is still a work-in-progress emulator, but several important gaps have already been closed.
Recent improvements include:
  • ADD SP, r8 (0xE8) implemented
  • delayed EI / IME enable behavior
  • HALT bug handling for pending interrupts
  • Serial interrupt vector support
  • basic serial transfer registers (FF01 / FF02)
  • basic MBC3 RTC register support
  • MBC3 RTC persistence across reloads
  • timer register synchronization
  • deferred TIMA reload after overflow
  • LY reset behavior on FF44 writes
  • OAM blocking during DMA
  • VRAM / OAM access restrictions based on PPU mode
Known Limitations
JS-Boy is not a cycle-accurate emulator yet.
Known gaps and risks include:
  • compatibility is still incomplete across commercial ROMs
  • PPU and DMA timing are improved, but still simplified
  • MBC3 RTC support is basic, not fully hardware-accurate
  • Color Game Boy support is still missing
  • some cartridge types are still unsupported
  • audio emulation is functional but not hardware-accurate
UI Language Support
The UI can be switched between German and English from the language selector in the right-side panel.
Currently translated:
  • splash text
  • storage / controls panel labels
  • ROM loading label
  • CPU status heading
  • save / load status messages
Saving
JS-Boy stores save RAM in localStorage per ROM checksum.
For MBC3 cartridges, RTC state is also stored separately in localStorage.
Development Notes
The emulator core currently lives in:
The UI entry points are:
License
No license has been added yet.
About
Browser-based Game Boy emulator UI with a custom JavaScript emulator core
Resources
Readme
Activity
Stars
0 stars
Watchers
0 watching
Forks
0 forks
Report repository
Releases
Packages
Contributors
Languages

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Force GitHub README to respect dark mode\n(function() {\n var style = document.createElement('style');\n style.textContent = '\n .markdown-body {\n color-scheme: dark light;\n }\n .markdown-body pre { background: #161b22 !important; }\n .markdown-body code { background: rgba(110, 118, 129, 0.4) !important; }\n .markdown-body table th, .markdown-body table td { border-color: #30363d !important; }\n .markdown-body img { background: #0d1117; }\n .markdown-body blockquote { border-left-color: #8b949e; }\n .markdown-body hr { border-color: #30363d; }\n ';\n document.head.appendChild(style);\n})();", "GitHub Dark Mode README Fix");
}
} catch(__e) { console.warn('[Userscript:GitHub Dark Mode README Fix]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
BranchesTags
Latest commit
History
20 Commits
Folders and files
NameName
Last commit message
Last commit date
lib
lib
README.md
README.md
README_de.md
README_de.md
app.js
app.js
index.html
index.html
style.css
style.css
Repository files navigation
JS-Boy
Lies mich auf Deutsch: README_de.md
JS-Boy is a browser-based Game Boy emulator UI with a custom JavaScript emulator core.
The main branch is the stable branch and is intended to back the GitHub Pages deployment of the project.
An experimental Game Boy Color branch is available at feat/cgb-core. That branch contains ongoing CGB work and may be more unstable than main.
The project started as a single HTML file and was later split into a cleaner GitHub-friendly structure:
  • index.html for markup
  • style.css for the Game Boy UI styling
  • app.js for UI wiring, i18n, ROM loading, and save import/export
  • lib/emulator.js for the emulator core
Features
  • Game Boy-style browser UI
  • ROM loading from the browser
  • Save RAM import/export (.sav)
  • Local save persistence via localStorage
  • Basic multi-language UI support

    • German
    • English
  • Custom emulator core with:

    • CPU
    • MMU
    • Timer
    • PPU
    • APU
    • Joypad
    • MBC1 / MBC3 / MBC5 support
Project Structure
.
|-- index.html
|-- style.css
|-- app.js
`-- lib/
`-- emulator.js

Running Locally
Because the app uses ES modules, you should serve it through a local web server instead of opening index.html directly as a file.
Example with Python:
python -m http.server 8000
Then open:
http://localhost:8000

Controls
  • D-pad: Arrow keys or WASD
  • A: Z, Y, or J
  • B: X or K
  • START: Enter
  • SELECT: Right Shift
Current Emulator Status
This is still a work-in-progress emulator, but several important gaps have already been closed.
Recent improvements include:
  • ADD SP, r8 (0xE8) implemented
  • delayed EI / IME enable behavior
  • HALT bug handling for pending interrupts
  • Serial interrupt vector support
  • basic serial transfer registers (FF01 / FF02)
  • basic MBC3 RTC register support
  • MBC3 RTC persistence across reloads
  • timer register synchronization
  • deferred TIMA reload after overflow
  • LY reset behavior on FF44 writes
  • OAM blocking during DMA
  • VRAM / OAM access restrictions based on PPU mode
Known Limitations
JS-Boy is not a cycle-accurate emulator yet.
Known gaps and risks include:
  • compatibility is still incomplete across commercial ROMs
  • PPU and DMA timing are improved, but still simplified
  • MBC3 RTC support is basic, not fully hardware-accurate
  • Color Game Boy support is still missing
  • some cartridge types are still unsupported
  • audio emulation is functional but not hardware-accurate
UI Language Support
The UI can be switched between German and English from the language selector in the right-side panel.
Currently translated:
  • splash text
  • storage / controls panel labels
  • ROM loading label
  • CPU status heading
  • save / load status messages
Saving
JS-Boy stores save RAM in localStorage per ROM checksum.
For MBC3 cartridges, RTC state is also stored separately in localStorage.
Development Notes
The emulator core currently lives in:
The UI entry points are:
License
No license has been added yet.
About
Browser-based Game Boy emulator UI with a custom JavaScript emulator core
Resources
Readme
Activity
Stars
0 stars
Watchers
0 watching
Forks
0 forks
Report repository
Releases
Packages
Contributors
Languages

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Highlight search terms from Google/DuckDuckGo/Bing referrer\n(function() {\n var ref = document.referrer;\n var terms = [];\n \n if (ref.includes('google.com') || ref.includes('duckduckgo.com') || ref.includes('bing.com')) {\n var url = new URL(ref);\n var q = url.searchParams.get('q') || url.searchParams.get('p');\n if (q) {\n terms = q.split(/\\s+/).filter(function(t) { return t.length > 2; });\n }\n }\n \n if (terms.length === 0) return;\n \n var style = document.createElement('style');\n style.textContent = '.userscript-highlight { background: #fbbf24; color: #1a1a2e; padding: 1px 3px; border-radius: 2px; }';\n document.head.appendChild(style);\n \n function highlight(node) {\n if (node.nodeType === 3) { // text node\n var text = node.textContent;\n var found = false;\n terms.forEach(function(term) {\n var regex = new RegExp('(' + term.replace(/[.*+?^${}()|[\\]\\\\]/g, '\\\\') + ')', 'gi');\n if (regex.test(text)) {\n found = true;\n var frag = document.createDocumentFragment();\n var parts = text.split(regex);\n parts.forEach(function(part, i) {\n if (i % 2 === 0) {\n frag.appendChild(document.createTextNode(part));\n } else {\n var span = document.createElement('span');\n span.className = 'userscript-highlight';\n span.textContent = part;\n frag.appendChild(span);\n }\n });\n node.parentNode.replaceChild(frag, node);\n }\n });\n } else if (node.nodeType === 1 && node.childNodes) { // element\n var skipTags = ['SCRIPT', 'STYLE', 'NOSCRIPT', 'TEXTAREA', 'INPUT', 'SELECT'];\n if (!skipTags.includes(node.tagName)) {\n Array.from(node.childNodes).forEach(highlight);\n }\n }\n }\n \n highlight(document.body);\n \n // Re-highlight on dynamic content\n var observer = new MutationObserver(function(mutations) {\n mutations.forEach(function(m) {\n m.addedNodes.forEach(function(node) {\n if (node.nodeType === 1 || node.nodeType === 3) highlight(node);\n });\n });\n });\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Highlight Search Terms");
}
} catch(__e) { console.warn('[Userscript:Highlight Search Terms]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
BranchesTags
Latest commit
History
20 Commits
Folders and files
NameName
Last commit message
Last commit date
lib
lib
README.md
README.md
README_de.md
README_de.md
app.js
app.js
index.html
index.html
style.css
style.css
Repository files navigation
JS-Boy
Lies mich auf Deutsch: README_de.md
JS-Boy is a browser-based Game Boy emulator UI with a custom JavaScript emulator core.
The main branch is the stable branch and is intended to back the GitHub Pages deployment of the project.
An experimental Game Boy Color branch is available at feat/cgb-core. That branch contains ongoing CGB work and may be more unstable than main.
The project started as a single HTML file and was later split into a cleaner GitHub-friendly structure:
  • index.html for markup
  • style.css for the Game Boy UI styling
  • app.js for UI wiring, i18n, ROM loading, and save import/export
  • lib/emulator.js for the emulator core
Features
  • Game Boy-style browser UI
  • ROM loading from the browser
  • Save RAM import/export (.sav)
  • Local save persistence via localStorage
  • Basic multi-language UI support

    • German
    • English
  • Custom emulator core with:

    • CPU
    • MMU
    • Timer
    • PPU
    • APU
    • Joypad
    • MBC1 / MBC3 / MBC5 support
Project Structure
.
|-- index.html
|-- style.css
|-- app.js
`-- lib/
`-- emulator.js

Running Locally
Because the app uses ES modules, you should serve it through a local web server instead of opening index.html directly as a file.
Example with Python:
python -m http.server 8000
Then open:
http://localhost:8000

Controls
  • D-pad: Arrow keys or WASD
  • A: Z, Y, or J
  • B: X or K
  • START: Enter
  • SELECT: Right Shift
Current Emulator Status
This is still a work-in-progress emulator, but several important gaps have already been closed.
Recent improvements include:
  • ADD SP, r8 (0xE8) implemented
  • delayed EI / IME enable behavior
  • HALT bug handling for pending interrupts
  • Serial interrupt vector support
  • basic serial transfer registers (FF01 / FF02)
  • basic MBC3 RTC register support
  • MBC3 RTC persistence across reloads
  • timer register synchronization
  • deferred TIMA reload after overflow
  • LY reset behavior on FF44 writes
  • OAM blocking during DMA
  • VRAM / OAM access restrictions based on PPU mode
Known Limitations
JS-Boy is not a cycle-accurate emulator yet.
Known gaps and risks include:
  • compatibility is still incomplete across commercial ROMs
  • PPU and DMA timing are improved, but still simplified
  • MBC3 RTC support is basic, not fully hardware-accurate
  • Color Game Boy support is still missing
  • some cartridge types are still unsupported
  • audio emulation is functional but not hardware-accurate
UI Language Support
The UI can be switched between German and English from the language selector in the right-side panel.
Currently translated:
  • splash text
  • storage / controls panel labels
  • ROM loading label
  • CPU status heading
  • save / load status messages
Saving
JS-Boy stores save RAM in localStorage per ROM checksum.
For MBC3 cartridges, RTC state is also stored separately in localStorage.
Development Notes
The emulator core currently lives in:
The UI entry points are:
License
No license has been added yet.
About
Browser-based Game Boy emulator UI with a custom JavaScript emulator core
Resources
Readme
Activity
Stars
0 stars
Watchers
0 watching
Forks
0 forks
Report repository
Releases
Packages
Contributors
Languages

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Strip utm_, fbclid, gclid, etc. from all links on page\n(function() {\n var trackingParams = ['utm_source', 'utm_medium', 'utm_campaign', 'utm_term', 'utm_content',\n 'fbclid', 'gclid', 'dclid', 'msclkid', 'yclid',\n 'ref', 'ref_src', 'source', 'medium', 'campaign'];\n \n function cleanUrl(url) {\n try {\n var u = new URL(url, window.location.origin);\n var changed = false;\n trackingParams.forEach(function(p) {\n if (u.searchParams.has(p)) {\n u.searchParams.delete(p);\n changed = true;\n }\n });\n return changed ? u.toString() : url;\n } catch (e) {\n return url;\n }\n }\n \n function cleanLinks() {\n document.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n \n cleanLinks();\n \n var observer = new MutationObserver(function(mutations) {\n mutations.forEach(function(m) {\n m.addedNodes.forEach(function(node) {\n if (node.nodeType === 1) {\n if (node.tagName === 'A') cleanLinks();\n node.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n });\n });\n });\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Remove Tracking Parameters from Links");
}
} catch(__e) { console.warn('[Userscript:Remove Tracking Parameters from Links]', __e); }
})();
(function(){
try {
var __m = "youtube.com";
var __re = new RegExp('^' + "youtube\\.com" + '

Skip to content
BranchesTags
Latest commit
History
20 Commits
Folders and files
NameName
Last commit message
Last commit date
lib
lib
README.md
README.md
README_de.md
README_de.md
app.js
app.js
index.html
index.html
style.css
style.css
Repository files navigation
JS-Boy
Lies mich auf Deutsch: README_de.md
JS-Boy is a browser-based Game Boy emulator UI with a custom JavaScript emulator core.
The main branch is the stable branch and is intended to back the GitHub Pages deployment of the project.
An experimental Game Boy Color branch is available at feat/cgb-core. That branch contains ongoing CGB work and may be more unstable than main.
The project started as a single HTML file and was later split into a cleaner GitHub-friendly structure:
  • index.html for markup
  • style.css for the Game Boy UI styling
  • app.js for UI wiring, i18n, ROM loading, and save import/export
  • lib/emulator.js for the emulator core
Features
  • Game Boy-style browser UI
  • ROM loading from the browser
  • Save RAM import/export (.sav)
  • Local save persistence via localStorage
  • Basic multi-language UI support

    • German
    • English
  • Custom emulator core with:

    • CPU
    • MMU
    • Timer
    • PPU
    • APU
    • Joypad
    • MBC1 / MBC3 / MBC5 support
Project Structure
.
|-- index.html
|-- style.css
|-- app.js
`-- lib/
`-- emulator.js

Running Locally
Because the app uses ES modules, you should serve it through a local web server instead of opening index.html directly as a file.
Example with Python:
python -m http.server 8000
Then open:
http://localhost:8000

Controls
  • D-pad: Arrow keys or WASD
  • A: Z, Y, or J
  • B: X or K
  • START: Enter
  • SELECT: Right Shift
Current Emulator Status
This is still a work-in-progress emulator, but several important gaps have already been closed.
Recent improvements include:
  • ADD SP, r8 (0xE8) implemented
  • delayed EI / IME enable behavior
  • HALT bug handling for pending interrupts
  • Serial interrupt vector support
  • basic serial transfer registers (FF01 / FF02)
  • basic MBC3 RTC register support
  • MBC3 RTC persistence across reloads
  • timer register synchronization
  • deferred TIMA reload after overflow
  • LY reset behavior on FF44 writes
  • OAM blocking during DMA
  • VRAM / OAM access restrictions based on PPU mode
Known Limitations
JS-Boy is not a cycle-accurate emulator yet.
Known gaps and risks include:
  • compatibility is still incomplete across commercial ROMs
  • PPU and DMA timing are improved, but still simplified
  • MBC3 RTC support is basic, not fully hardware-accurate
  • Color Game Boy support is still missing
  • some cartridge types are still unsupported
  • audio emulation is functional but not hardware-accurate
UI Language Support
The UI can be switched between German and English from the language selector in the right-side panel.
Currently translated:
  • splash text
  • storage / controls panel labels
  • ROM loading label
  • CPU status heading
  • save / load status messages
Saving
JS-Boy stores save RAM in localStorage per ROM checksum.
For MBC3 cartridges, RTC state is also stored separately in localStorage.
Development Notes
The emulator core currently lives in:
The UI entry points are:
License
No license has been added yet.
About
Browser-based Game Boy emulator UI with a custom JavaScript emulator core
Resources
Readme
Activity
Stars
0 stars
Watchers
0 watching
Forks
0 forks
Report repository
Releases
Packages
Contributors
Languages

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Auto-enable theater mode on YouTube\n(function() {\n function tryTheater() {\n var btn = document.querySelector('button[aria-label=\"Theater mode\"], ytd-player #player button[title=\"Theater mode\"]');\n if (btn && !btn.classList.contains('activated')) {\n btn.click();\n }\n }\n \n // Try immediately\n tryTheater();\n \n // Try after navigation (SPA)\n var lastUrl = location.href;\n setInterval(function() {\n if (location.href !== lastUrl) {\n lastUrl = location.href;\n setTimeout(tryTheater, 500);\n }\n }, 1000);\n \n // Also try on player load\n var observer = new MutationObserver(tryTheater);\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "YouTube Theater Mode Default");
}
} catch(__e) { console.warn('[Userscript:YouTube Theater Mode Default]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
BranchesTags
Latest commit
History
20 Commits
Folders and files
NameName
Last commit message
Last commit date
lib
lib
README.md
README.md
README_de.md
README_de.md
app.js
app.js
index.html
index.html
style.css
style.css
Repository files navigation
JS-Boy
Lies mich auf Deutsch: README_de.md
JS-Boy is a browser-based Game Boy emulator UI with a custom JavaScript emulator core.
The main branch is the stable branch and is intended to back the GitHub Pages deployment of the project.
An experimental Game Boy Color branch is available at feat/cgb-core. That branch contains ongoing CGB work and may be more unstable than main.
The project started as a single HTML file and was later split into a cleaner GitHub-friendly structure:
  • index.html for markup
  • style.css for the Game Boy UI styling
  • app.js for UI wiring, i18n, ROM loading, and save import/export
  • lib/emulator.js for the emulator core
Features
  • Game Boy-style browser UI
  • ROM loading from the browser
  • Save RAM import/export (.sav)
  • Local save persistence via localStorage
  • Basic multi-language UI support

    • German
    • English
  • Custom emulator core with:

    • CPU
    • MMU
    • Timer
    • PPU
    • APU
    • Joypad
    • MBC1 / MBC3 / MBC5 support
Project Structure
.
|-- index.html
|-- style.css
|-- app.js
`-- lib/
`-- emulator.js

Running Locally
Because the app uses ES modules, you should serve it through a local web server instead of opening index.html directly as a file.
Example with Python:
python -m http.server 8000
Then open:
http://localhost:8000

Controls
  • D-pad: Arrow keys or WASD
  • A: Z, Y, or J
  • B: X or K
  • START: Enter
  • SELECT: Right Shift
Current Emulator Status
This is still a work-in-progress emulator, but several important gaps have already been closed.
Recent improvements include:
  • ADD SP, r8 (0xE8) implemented
  • delayed EI / IME enable behavior
  • HALT bug handling for pending interrupts
  • Serial interrupt vector support
  • basic serial transfer registers (FF01 / FF02)
  • basic MBC3 RTC register support
  • MBC3 RTC persistence across reloads
  • timer register synchronization
  • deferred TIMA reload after overflow
  • LY reset behavior on FF44 writes
  • OAM blocking during DMA
  • VRAM / OAM access restrictions based on PPU mode
Known Limitations
JS-Boy is not a cycle-accurate emulator yet.
Known gaps and risks include:
  • compatibility is still incomplete across commercial ROMs
  • PPU and DMA timing are improved, but still simplified
  • MBC3 RTC support is basic, not fully hardware-accurate
  • Color Game Boy support is still missing
  • some cartridge types are still unsupported
  • audio emulation is functional but not hardware-accurate
UI Language Support
The UI can be switched between German and English from the language selector in the right-side panel.
Currently translated:
  • splash text
  • storage / controls panel labels
  • ROM loading label
  • CPU status heading
  • save / load status messages
Saving
JS-Boy stores save RAM in localStorage per ROM checksum.
For MBC3 cartridges, RTC state is also stored separately in localStorage.
Development Notes
The emulator core currently lives in:
The UI entry points are:
License
No license has been added yet.
About
Browser-based Game Boy emulator UI with a custom JavaScript emulator core
Resources
Readme
Activity
Stars
0 stars
Watchers
0 watching
Forks
0 forks
Report repository
Releases
Packages
Contributors
Languages

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Remove or un-stick sticky/fixed headers that block content\n(function() {\n function unstick() {\n document.querySelectorAll('header, nav, [role=\"banner\"], .header, .navbar, .sticky, .fixed-top, [style*=\"position: fixed\"], [style*=\"position:sticky\"]').forEach(function(el) {\n if (el.style.position === 'fixed' || el.style.position === 'sticky' || \n getComputedStyle(el).position === 'fixed' || getComputedStyle(el).position === 'sticky') {\n el.style.position = 'static';\n el.style.top = 'auto';\n el.style.zIndex = 'auto';\n }\n });\n }\n \n unstick();\n \n var observer = new MutationObserver(unstick);\n observer.observe(document.body, { childList: true, subtree: true, attributes: true, attributeFilter: ['style', 'class'] });\n})();", "Kill Sticky Headers");
}
} catch(__e) { console.warn('[Userscript:Kill Sticky Headers]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
BranchesTags
Latest commit
History
20 Commits
Folders and files
NameName
Last commit message
Last commit date
lib
lib
README.md
README.md
README_de.md
README_de.md
app.js
app.js
index.html
index.html
style.css
style.css
Repository files navigation
JS-Boy
Lies mich auf Deutsch: README_de.md
JS-Boy is a browser-based Game Boy emulator UI with a custom JavaScript emulator core.
The main branch is the stable branch and is intended to back the GitHub Pages deployment of the project.
An experimental Game Boy Color branch is available at feat/cgb-core. That branch contains ongoing CGB work and may be more unstable than main.
The project started as a single HTML file and was later split into a cleaner GitHub-friendly structure:
  • index.html for markup
  • style.css for the Game Boy UI styling
  • app.js for UI wiring, i18n, ROM loading, and save import/export
  • lib/emulator.js for the emulator core
Features
  • Game Boy-style browser UI
  • ROM loading from the browser
  • Save RAM import/export (.sav)
  • Local save persistence via localStorage
  • Basic multi-language UI support

    • German
    • English
  • Custom emulator core with:

    • CPU
    • MMU
    • Timer
    • PPU
    • APU
    • Joypad
    • MBC1 / MBC3 / MBC5 support
Project Structure
.
|-- index.html
|-- style.css
|-- app.js
`-- lib/
`-- emulator.js

Running Locally
Because the app uses ES modules, you should serve it through a local web server instead of opening index.html directly as a file.
Example with Python:
python -m http.server 8000
Then open:
http://localhost:8000

Controls
  • D-pad: Arrow keys or WASD
  • A: Z, Y, or J
  • B: X or K
  • START: Enter
  • SELECT: Right Shift
Current Emulator Status
This is still a work-in-progress emulator, but several important gaps have already been closed.
Recent improvements include:
  • ADD SP, r8 (0xE8) implemented
  • delayed EI / IME enable behavior
  • HALT bug handling for pending interrupts
  • Serial interrupt vector support
  • basic serial transfer registers (FF01 / FF02)
  • basic MBC3 RTC register support
  • MBC3 RTC persistence across reloads
  • timer register synchronization
  • deferred TIMA reload after overflow
  • LY reset behavior on FF44 writes
  • OAM blocking during DMA
  • VRAM / OAM access restrictions based on PPU mode
Known Limitations
JS-Boy is not a cycle-accurate emulator yet.
Known gaps and risks include:
  • compatibility is still incomplete across commercial ROMs
  • PPU and DMA timing are improved, but still simplified
  • MBC3 RTC support is basic, not fully hardware-accurate
  • Color Game Boy support is still missing
  • some cartridge types are still unsupported
  • audio emulation is functional but not hardware-accurate
UI Language Support
The UI can be switched between German and English from the language selector in the right-side panel.
Currently translated:
  • splash text
  • storage / controls panel labels
  • ROM loading label
  • CPU status heading
  • save / load status messages
Saving
JS-Boy stores save RAM in localStorage per ROM checksum.
For MBC3 cartridges, RTC state is also stored separately in localStorage.
Development Notes
The emulator core currently lives in:
The UI entry points are:
License
No license has been added yet.
About
Browser-based Game Boy emulator UI with a custom JavaScript emulator core
Resources
Readme
Activity
Stars
0 stars
Watchers
0 watching
Forks
0 forks
Report repository
Releases
Packages
Contributors
Languages

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Universal Dark Mode - works on any site\n(function() {\n var enabled = true;\n \n function applyDarkMode() {\n if (!enabled) return;\n \n // Create style element if it doesn't exist\n var style = document.getElementById('universal-dark-mode-style');\n if (!style) {\n style = document.createElement('style');\n style.id = 'universal-dark-mode-style';\n document.head.appendChild(style);\n }\n \n // Dark mode CSS - inverts colors but preserves images/video\n style.textContent = '\n /* Invert everything except media */\n html {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #1a1a2e !important;\n }\n \n /* Restore images, videos, iframes, canvas */\n img, video, iframe, canvas, svg, picture, [style*=\"background-image\"] {\n filter: invert(1) hue-rotate(180deg) !important;\n }\n \n /* Preserve specific elements that should not be inverted */\n .no-dark-mode, .no-dark-mode *,\n [data-theme=\"light\"], [data-theme=\"light\"],\n .ace_editor, .ace_editor *,\n .CodeMirror, .CodeMirror *,\n .monaco-editor, .monaco-editor *,\n .markdown-body pre, .markdown-body pre *,\n .highlight, .highlight *,\n pre code, pre code * {\n filter: none !important;\n }\n \n /* Fix common UI elements */\n .modal, .popup, .dropdown-menu, .tooltip, .popover {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #2d2d44 !important;\n border-color: #444 !important;\n }\n \n /* Scrollbars */\n ::-webkit-scrollbar { background: #1a1a2e !important; }\n ::-webkit-scrollbar-thumb { background: #444 !important; }\n ::-webkit-scrollbar-thumb:hover { background: #555 !important; }\n \n /* Selection */\n ::selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ::-moz-selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ';\n }\n \n function removeDarkMode() {\n var style = document.getElementById('universal-dark-mode-style');\n if (style) style.remove();\n }\n \n // Toggle with Alt+Shift+D\n document.addEventListener('keydown', function(e) {\n if (e.altKey && e.shiftKey && e.key === 'D') {\n e.preventDefault();\n enabled = !enabled;\n if (enabled) {\n applyDarkMode();\n console.log('[Universal Dark Mode] Enabled');\n } else {\n removeDarkMode();\n console.log('[Universal Dark Mode] Disabled');\n }\n }\n });\n \n // Apply on load\n applyDarkMode();\n \n // Re-apply on dynamic content\n var observer = new MutationObserver(function(mutations) {\n if (enabled && !document.getElementById('universal-dark-mode-style')) {\n applyDarkMode();\n }\n });\n observer.observe(document.head, { childList: true });\n \n console.log('[Universal Dark Mode] Loaded - Press Alt+Shift+D to toggle');\n})();", "Universal Dark Mode");
}
} catch(__e) { console.warn('[Userscript:Universal Dark Mode]', __e); }
})();
})();

Skip to content
BranchesTags
Latest commit
History
20 Commits
Folders and files
NameName
Last commit message
Last commit date
lib
lib
README.md
README.md
README_de.md
README_de.md
app.js
app.js
index.html
index.html
style.css
style.css
Repository files navigation
JS-Boy
Lies mich auf Deutsch: README_de.md
JS-Boy is a browser-based Game Boy emulator UI with a custom JavaScript emulator core.
The main branch is the stable branch and is intended to back the GitHub Pages deployment of the project.
An experimental Game Boy Color branch is available at feat/cgb-core. That branch contains ongoing CGB work and may be more unstable than main.
The project started as a single HTML file and was later split into a cleaner GitHub-friendly structure:
  • index.html for markup
  • style.css for the Game Boy UI styling
  • app.js for UI wiring, i18n, ROM loading, and save import/export
  • lib/emulator.js for the emulator core
Features
  • Game Boy-style browser UI
  • ROM loading from the browser
  • Save RAM import/export (.sav)
  • Local save persistence via localStorage
  • Basic multi-language UI support

    • German
    • English
  • Custom emulator core with:

    • CPU
    • MMU
    • Timer
    • PPU
    • APU
    • Joypad
    • MBC1 / MBC3 / MBC5 support
Project Structure
.
|-- index.html
|-- style.css
|-- app.js
`-- lib/
`-- emulator.js

Running Locally
Because the app uses ES modules, you should serve it through a local web server instead of opening index.html directly as a file.
Example with Python:
python -m http.server 8000
Then open:
http://localhost:8000

Controls
  • D-pad: Arrow keys or WASD
  • A: Z, Y, or J
  • B: X or K
  • START: Enter
  • SELECT: Right Shift
Current Emulator Status
This is still a work-in-progress emulator, but several important gaps have already been closed.
Recent improvements include:
  • ADD SP, r8 (0xE8) implemented
  • delayed EI / IME enable behavior
  • HALT bug handling for pending interrupts
  • Serial interrupt vector support
  • basic serial transfer registers (FF01 / FF02)
  • basic MBC3 RTC register support
  • MBC3 RTC persistence across reloads
  • timer register synchronization
  • deferred TIMA reload after overflow
  • LY reset behavior on FF44 writes
  • OAM blocking during DMA
  • VRAM / OAM access restrictions based on PPU mode
Known Limitations
JS-Boy is not a cycle-accurate emulator yet.
Known gaps and risks include:
  • compatibility is still incomplete across commercial ROMs
  • PPU and DMA timing are improved, but still simplified
  • MBC3 RTC support is basic, not fully hardware-accurate
  • Color Game Boy support is still missing
  • some cartridge types are still unsupported
  • audio emulation is functional but not hardware-accurate
UI Language Support
The UI can be switched between German and English from the language selector in the right-side panel.
Currently translated:
  • splash text
  • storage / controls panel labels
  • ROM loading label
  • CPU status heading
  • save / load status messages
Saving
JS-Boy stores save RAM in localStorage per ROM checksum.
For MBC3 cartridges, RTC state is also stored separately in localStorage.
Development Notes
The emulator core currently lives in:
The UI entry points are:
License
No license has been added yet.
About
Browser-based Game Boy emulator UI with a custom JavaScript emulator core
Resources
Readme
Activity
Stars
0 stars
Watchers
0 watching
Forks
0 forks
Report repository
Releases
Packages
Contributors
Languages