Cars · Rom

Crome JavaScript scripting API

Reference for the legacy Crome ROM editor JavaScript API used by scripts, ROM handlers, and plug-ins.

Updated June 15, 2026 Advanced

Adapted from pgmfi.org wiki

Crome exposes a JavaScript API for extending the legacy OBD1 ROM editor with scripts, ROM handlers, and plug-ins. This reference preserves the API documented by the original Crome community.

Warning

Work on a copy of the ROM and verify every output before installing it in an ECU. API behavior can differ between Crome versions, and an incorrect script can corrupt tables, scalars, or checksums.

Accessing API objects

Inside a Crome script, members of the default window object can be called directly or through window:

refresh();
window.refresh();
rom.byteAt(0x7FFF);
window.rom.byteAt(0x7FFF);

An HTML-based Crome plug-in accesses the same objects through window.external:

window.external.refresh();
window.external.rom.byteAt(0x7FFF);

The archived documentation describes three main objects:

Object	Purpose
`window`	Dialogs, plug-in registration, external commands, and display refresh
`window.rom` / `rom`	Read and modify the active ROM, tables, scalars, and feature flags
`window.files` / `files`	Open, save, read, and write files

Window functions

Function	Documented purpose
`addRomHandler(romtype, author, jscmd)`	Register a handler for a ROM type
`addPlugin(author, mnucaption, jscmd, category)`	Add an entry to Crome's plug-in menu
`alert(msg)`	Display a message with an OK button
`confirm(msg)`	Display a Yes/No confirmation; returns false or true
`DecToHex(dec)`	Convert a decimal value to a hexadecimal string
`exal(cipherstring)`	Evaluate an encoded JavaScript string
`GetFilePath(filename)`	Return the path portion of a filename
`GetFileName(filename)`	Return the name portion of a filename
`HiByte(w)`	Return the high byte of a word
`LoByte(w)`	Return the low byte of a word
`input(msg, options, values)`	Display an input selection dialog
`include(filename)`	Include another script file
`prompt(caption, msg, default)`	Prompt for a response
`select(prompt, selection)`	Return the selected item index, or `-1` when cancelled
`shell(filename, params, windowstate)`	Start an external application
`shelld(doscmd)`	Run a DOS command and return its output
`shellw(filename, params, windowstate)`	Start an application and wait for it to close
`showBrowser(url, width, height)`	Open Crome's built-in browser
`refresh()`	Refresh the editor after a script changes the active ROM

Note

The archived signature declares prompt() as returning a boolean, while its description says it returns the user's response or an empty string. Verify behavior in the Crome version being targeted.

Examples from the archived API:

addRomHandler(rtP30, 'Author', '_handle_p30_rom()');
addPlugin('Author', 'Test Plugin', '_run_test_plugin()', 0);
shell('notepad.exe', 'C:\\autoexec.bat', 0);
showBrowser('my_html_plugin.html', 400, 250);

An older quick reference also lists _rom_write(start, values, count) and _rom_fill(fromAddr, toAddr, byteFill), plus a rom.type property with examples such as rp30, rp72, rp28, and rpCustom. Their availability is version-dependent.

ROM object

Byte, word, and table access

Member	Access	Documented purpose
`byteAt(addr)`	Read/write	Get or set one byte at a ROM address
`wordAt(addr)`	Read/write	Get or set a little-endian word at a ROM address
`working_table`	Read/write	Select the active fuel or ignition table
`tableByte(col, row)`	Read/write	Get or set a raw byte in the active table
`tableValue(col, row)`	Read/write	Get or set the interpreted table value
`tableWidth`	Read-only	Width of the active table
`tableHeight`	Read-only	Height of the active table
`mapScalar(table, col)`	Read/write	Get or set a MAP scalar in millibars
`revScalar(table, row)`	Read/write	Get or set an RPM scalar

working_table uses these documented values:

Value	Table
`0`	Low fuel
`1`	High fuel
`2`	Low ignition
`3`	High ignition

rom.working_table = 2;
var ignitionByte = rom.tableByte(0, 5);

var lastByte = rom.byteAt(0x7FFF);
rom.byteAt(0x7FFF) = 0xFF;

wordAt() accounts for little-endian storage. The source says bytes stored as [0xAB][0xCD] are returned as 0xCDAB.

ROM metadata and feature flags

Member	Access	Documented meaning
`addressOf(name)`	Read/write	Address stored in a named special register
`addressIn(index)`	Read/write	Address stored in special-register index `0` through `63`
`base`	Read/write	Base ROM used for default address locations
`title`	Read/write	Text shown in Crome's status bar
`filename`	Read-only	Full filename of the active ROM
`OBDMode`	Read/write	Formula mode: `0` OBD0, `1` OBD1, `2` OBD2, `3` unknown
`notes`	Read/write	Notes attached to the active ROM
`gup()`	Function	Create a group undo point around a multi-change operation

Feature flags are documented as read/write byte properties:

Property	Values
`hasLaunchControl`	`0` off, `1` on
`hasFullThrottleShift`	`0` off, `1` on
`hasBoost`	`0` none, `1` stock MAP boost, `2` 3-bar boost, `3` custom
`hasFinalMultiplier`	`0` off, `1` on
`hasShiftLight`	`0` off, `1` on
`hasIAB`	`0` off, `1` on

Use gup() before and after a group of changes so Crome can undo them as one action:

rom.gup();
for (var i = 0; i <= 0x7FFF; i++) {
    rom.byteAt(i) = LoByte(i);
}
rom.gup();
refresh();

Files object

Member	Documented purpose
`showSave(filter, filterindex)`	Show a save dialog and return the selected filename
`showOpen(filter, filterindex)`	Show an open dialog and return the selected filename
`exists(filename)`	Return true when a file exists
`getFile(filename)`	Read a text file
`putFile(filename, data)`	Write data to a file
`browseFolder`	Show a folder browser and return the selected path

Cancelled open, save, and folder dialogs are documented as returning an empty string.

Special register names

Use these names with rom.addressOf('NAME') or their numeric index with rom.addressIn(index).

Name	Index	Documented purpose
`CHECKSUM`	0	Checksum correction address
`LOW_MAP_SCALAR`	1	Low MAP scalar address
`HIGH_MAP_SCALAR`	2	High MAP scalar address
`LOW_REV_SCALAR`	3	Low RPM scalar address
`HIGH_REV_SCALAR`	4	High RPM scalar address
`LOW_FUEL`	5	Low fuel table address
`HIGH_FUEL`	6	High fuel table address
`LOW_IGNITION`	7	Low ignition table address
`HIGH_IGNITION`	8	High ignition table address
`NFO_LOW_TABLE`	9	Low-table dimensions; high byte is height, low byte is width
`NFO_HIGH_TABLE`	10	High-table dimensions; high byte is height, low byte is width
`REVCUT1`	11	First rev-cut value address
`REVRES1`	12	First rev-resume value address
`REVCUT2`	13	Second rev-cut value address
`REVRES2`	14	Second rev-resume value address
`VTEC_TABLE`	15	VTEC table address
`NFO_VTEC_TABLE`	16	VTEC table information
`VTEC`	17	VTEC configuration byte address
`IDLE`	25	Idle value address
`KNOCK`	26	Knock configuration byte address
`ELD`	27	ELD configuration byte address
`BARO`	29	Barometric-pressure configuration byte address
`VTECVSS`	30	VTEC VSS-check configuration byte address
`VTECCOOL`	31	VTEC coolant-check configuration byte address
`DEBUGMODE`	32	Debug-mode configuration byte address
`OXYHEAT`	33	O2-heater-check configuration byte address
`LAUNCH_CUT`	40	Launch-control cut value address
`LAUNCH_RES`	41	Launch-control resume value address
`SHIFT_CUT`	42	Full-throttle-shift cut value address
`SHIFT_RES`	43	Full-throttle-shift resume value address
`SPEED_LIMIT`	44	Speed-limiter value address
`NFO_MAP_MIN`	45	Minimum MAP information; no description in source
`NFO_MAP_MAX`	46	Maximum MAP information; no description in source
`MTX1`	50	Final fuel multiplier address
`MTX2`	51	No description in source
`MTX3`	52	Cranking fuel multiplier address
`MTX4`	53	No description in source
`MTX5`	54	Tip-in fuel multiplier address
`MTX6`	55	No description in source
`SL_BYTE`	56	Shift-light configuration byte address
`SL_RPM`	57	Shift-light RPM address

The archived documentation says a ROM handler must set the corresponding hasLaunchControl, hasFullThrottleShift, hasFinalMultiplier, hasShiftLight, and hasIAB properties to 1 for Crome's built-in option editors to use them.

Credits and source

Source Adapted from Crome Script on pgmfi.org wiki. Licensed under CC BY-NC-SA 1.0.

Accessing API objects#

Window functions#

ROM object#

Byte, word, and table access#

ROM metadata and feature flags#

Files object#

Special register names#