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Technical Information on use of the Emularity

To use this project you'll need to provide it with a canvas element, styled as necessary so that it has the correct size on screen (the emulated program will be scaled up automatically to fit, controlling for aspect ratio). You will also likely want to provide a simple UI for entering full-screen mode or muting the audio; these can simply call methods on the emulator when activated.

Emulator API

The Emulator constructor takes three arguments: a canvas element, an optional set of callbacks, and a config (as detailed below) or a function which returns a Promise of a config.

Acquiring Emulators

The Internet Archive is currently maintaining two sets of pre-built emulators - one for MAME and one for EM-DOSBOX. They can be found at:

Note that MESS and MAME used to be separate, if related, projects. They've recently been combined into a single source code repository and prjoject structure, and Emularity has changed to match.

Instructions for building these yourself will be added in the future.

The Scripted Amiga Emulator is much simpler to build, as it is already written in Javascript.



Arcade game

Loads the emulator for the arcade game 1943, and gives it a compressed copy of the rom (which it loads from examples/

  var emulator = new Emulator(document.querySelector("#canvas"),
                              new MAMELoader(MAMELoader.driver("1943"),
                                             MAMELoader.nativeResolution(224, 256),
                                                                  MAMELoader.fetchFile("Game File",
  emulator.start({ waitAfterDownloading: true });

Console game for Atari 2600

Loads the emulator for the Atari 2600 console, and an image of a catridge for Pitfall. Notice how we download the image, storing it in a file, then set up a "cart" peripheral so that the emulator can find it. We also load a configuration file that preconfigures some keybindings needed to use the 2600.

  var emulator = new Emulator(document.querySelector("#canvas"),
                              new MAMELoader(MAMELoader.driver("a2600"),
                                             MAMELoader.nativeResolution(352, 223),
                                                                  MAMELoader.fetchFile("Game File",
                                                                  MAMELoader.fetchFile("Config File",
                                             MAMELoader.peripheral("cart", "Pitfall_Activision_1982.bin")))
  emulator.setScale(3).start({ waitAfterDownloading: true });

DOS game

Here we load the DOSBox emulator, and a zip file containing the game ZZT which we decompress and then mount as the C drive. We also tell DosBox to immediately start running zzt.exe, which is inside the zip.

  var emulator = new Emulator(document.querySelector("#canvas"),
                              new DosBoxLoader(DosBoxLoader.emulatorJS("emulators/dosbox.js"),
                                               DosBoxLoader.nativeResolution(640, 400),
                                                                     DosBoxLoader.fetchFile("Game File",
  emulator.start({ waitAfterDownloading: true });

Amiga demo

The Amiga is interesting because several models had a split bios, requiring two bios images. We have to download them both, and then provide their names in the right order.

  var emulator = new Emulator(document.querySelector("#canvas"),
                              new SAELoader(SAELoader.model("A500"),
                                            SAELoader.nativeResolution(720, 568),
                                            SAELoader.rom(["aros-amiga-m68k-rom.bin", "aros-amiga-m68k-ext.bin"]),
                                            SAELoader.floppy(0, "Cool_Demos_17.2_1989_Razor_1911")))
  emulator.setScale(3).start({ waitAfterDownloading: true });

Configuration API

Currently there are three supported emulators, JSMESS, EM-DOSBox and SAE. JSMESS provides emulation for arcade games, consoles, and early personal computers. As this emulator supports such a wide variety of hardware it has been broken up into several dozen emulators each supporting one machine lest the resulting javascript be intractably large (60+ megabytes). EM-DOSBox provides emulation for software that runs on x86 PCs using the DOS operating systems common to the era. SAE emulates the Amiga computer system.

Each of these is configured by calling a constructor function and providing it with arguments formed by calling static methods on that same constructor. In principle this configuration is just an object with various properties. Although the static methods are more indirect, they are intended to allow autocompletion in IDEs to function, and thus make writing them more convenient.


  • BaseLoader.emulatorJS(url)
  • BaseLoader.emulatorWASM(url)
  • BaseLoader.mountZip(drive, file)
  • BaseLoader.mountFile(filename, file)
  • BaseLoader.fetchFile(url)
  • BaseLoader.fetchOptionalFile(url)
  • BaseLoader.localFile(data)


  • MAMELoader.driver(driverName)
  • MAMELoader.extraArgs(args)
  • MAMELoader.peripheral(name, filename)


JSMESSLoader is merely a synonym for MAMELoader, and is provided so that we don't break existing users.


  • DosBoxLoader.startExe(filename)
  • DosBoxLoader.extraArgs(args)


  • SAELoader.model(modelname)
  • SAELoader.fastMemory(megabytes)
  • SAELoader.rom(filenames)
  • SAELoader.floppy(index, filename)
  • SAELoader.ntsc(boolean)

Internet Archive

There's also a helper for loading software from the Internet Archive, IALoader. IALoader looks at the metadata associated with an Internet Archive item and uses that to build the configuration for the emulator by calling one of the other loaders as necessary.


You need only supply the canvas element and the Internet Archive's item name:

var emulator = new IALoader(document.querySelector("#canvas"),

Runtime API

Once you have an emulator object, there are several methods you can call.

  • start()
  • requestFullScreen()
  • mute()
  • unmute()
  • toggleMute()
  • setSplashColors()
  • others…

Splash Screen Styles

By default, Emularity requires no stylesheet; it directly styles every element that it creates instead. If you would like more control over how the splash screen looks than is provided by the setSplashColors method, pass { hasCustomCSS: true } to the start method. All of the splash screen elements will be unstyled, leaving the look up to you. For reference, the default styles normally applied by Emularity are approximately as follows:

.emularity-splash-screen {
  color: white;
  background-color: black;
  position: absolute;
  top: 0;
  left: 0;
  right: 0
.emularity-splash-screen .emularity-splash-image {
  display: block;
  margin-left: auto;
  margin-right: auto
.emularity-splash-screen .emularity-splash-title {
  display: block;
  width: 100%;
  margin-top: 1em;
  margin-bottom: 1em;
  text-align: center;
  font: 24px sans-serif
.emularity-splash-screen .emularity-progress-indicator {
  color: white;
  background-color: black;
  width: 75%;
  margin-left: auto;
  margin-right: auto;
  border-collapse: separate;
  border-spacing: 2px
.emularity-splash-screen .emularity-progress-indicator tr {
  text-align: center
.emularity-splash-screen .emularity-progress-indicator td {
  position: relative;
  padding-top: 4px
.emularity-splash-screen .emularity-progress-indicator td.emularity-download-success {
  font-weight: bold;
  color: black;
  background-color: white
.emularity-splash-screen .emularity-progress-indicator td.emularity-download-failure {
  font-weight: bold;
  color: black;
  background-color: red
.emularity-splash-screen .emularity-progress-indicator td .emularity-download-title {
  white-space: nowrap
.emularity-splash-screen .emularity-progress-indicator td .emularity-download-status {
  position: absolute;
  left: .5em