fomod

A JavaScript/TypeScript library for working with FOMOD installers both in the browser and in Node (via jsdom)

Important

You MUST make sure that any Document you provide uses a valid XML contentType, e.g. 'text/xml'. This is enforced at multiple levels for your own safety. The DOM behaves differently between the XML and HTML implementations and this can cause unexpected issues with Fomod installers.

How Do I Do This?

Browser

import { BlankModuleConfig } from 'https://unpkg.com/fomod';

const parser = new DOMParser()

parser.parseFromString(BlankModuleConfig, 'text/xml')

jsdom

import { BlankModuleConfig } from 'fomod';
import { JSDOM } from 'jsdom';

new JSDOM(BlankModuleConfig, {contentType: 'text/xml'});

What Is a FOMOD

FOMOD, which originally stood for FallOut MOD, is a confusingly-named file installer format pioneered by Fallout Mod Manager (FOMM). The goal of the format is to present users with options to be taken into account when installing the mod. It's primarily used in the Bethesda modding scene, though it's typically supported for use with any game a given mod manager supports. While FOMM, Nexus Mod Manager, and Vortex all supported writing a .NET installer (called a "scripted installer"), it's very rarely observed in use in the wild. With that and the security threat that comes with arbitrary code execution, most mod managers forego its support.

FOMOD installers are therefore nearly always written in the alternative, a schema-compliant XML file. This XML format is a little burdensome and a lot XML, so tools have popped up over the years to simplify their creation. Namely, GandaG's FOMOD Designer—a direct 1-to-1 editor and representation of the XML tree—and the FOMOD Creation Tool, a more abstract and arguably more user-friendly representation of the installer format. In development is the Fomod Builder, an attempt at meeting both in the middle by providing full schema-allowed control, helpful tooltips, a dark-mode UI, built-in mod manager previews & editor styles, and encouraging users to poke around in the XML as they use the tool.

Quick terminology breakdown

(I chose better names)

Term Used	Canonical Name	What It Refers To
Install	File/Folder	Files and folders that might be installed by the FOMOD
Step	Install Step	A bundle of Groups presented as a single page
Group	Group	A bundle of checkboxes or radio buttons presented as a section with a header
Option	Plugin	A single checkbox or radio button
Mod Manager Version Dependency	FOMM Dependency	A dependency on a specific version of a mod manager
Script Extender Version Dependency	FOSE Dependency	A dependency on a specific version of a script extender

What This Library Does

fomod is a library to parse, create, and edit FOMOD installers. It includes:

• Full support for the FOMOD specification
• Bundled type declarations, source maps, and source code
• Written in TypeScript and thoroughly unit-tested
• Helpful JSDoc comments detailing:
  • Usage
  • Quirks
  • Mod Manager Support
  • Defacto Deprecation
• Create New Installers & Components
• Parse Existing Installers & Components
• In-place editing of existing documents, be they from the native browser or jsdom.
  • You can force a fresh start by passing an empty Document object

    [!IMPORTANT] Documents will need to be explicitly decommissioned to prevent memory leaks when using large numbers of documents or allowing users to arbitrarily create them

• Dependencies on Options (via flags)
  • Options can be used as dependency within the codebase and are converted to a flag dependency when an XML document is produced

Why This Library Exists

Despite its age, the FOMOD format is incredibly popular and serves most everyone's needs. I wasn't a particular fan of the tooling, however—I found the existing solutions rather janky and unintuitive—and set out to create tooling of my own. I first attempted to write it in pure JavaScript, but I learned over time how foolish of an idea that was. I've since learned the error of my ways and written this here library. I intent to write a static Next.js site to host a revised FOMOD Builder using this very library.

As A Developer

If you're looking to use this library, this section will be your best friend.

At its core, each data structure (steps, options, installs, dependencies, etc.) is represented by a class.

If you're already familiar with the XML structure, each class generally represents one or two levels of element. For instance, the Option class represents the <plugin> element and the Group class represents <group> and <plugins>. This is done to reduce the amount of boilerplate you as a developer need to write while still giving you complete control over your installer.

The XmlRepresentation Class

This associates the element with this document! For most classes, this is free of side effects. For most classes, the element-document map does not restrict garbage collection. However, with certain classes (e.g. FlagInstance), this can lead to memory leaks. To prevent this, you can call the decommission method on the class.

The easiest way to make sure you're covered, especially between updates, is to always decommission the document (or class) when you're done with it. The decommission method is recursive; therefore, you should call it on the highest level class(es) you have access to. Typically, these will be fomod and fomodInfo.

Option Dependencies

This library provides a way to use an Option directly as the key for a FlagDependency. We'll handle the flag name and value for you, cutting out the flag middle-man from the developer's perspective.

Parsing/Serialization Configuration

The library includes a number of options to control how the XML is parsed and serialized. These can be passed into any XmlRepresentation subclass's XmlRepresentation.prototype.asElement() and XmlRepresentation.parse() methods as well as the parseModuleDoc() and parseInfoDoc() functions. Options:

Option	Type	Default	Description
includeInfoSchema	boolean or string	true	Whether or to include a third-party schema for Info.xml. If a string is provided, we'll use that string as the schema location. Otherwise, we'll use the library's default.
flattenConditionalInstalls	boolean	false	Whether to move all conditional installs with only a dependency on a single option to the tag of that option. Note that this may cause slight performance issues with Vortex on slower machines.
flattenConditionalInstallsNoDependencies	boolean	false	Whether to reorganize all conditional installs with no dependencies into the tag.
removeEmptyConditionalInstalls	boolean	true	Whether to remove conditional installs with no dependencies and no files (has no effect when flattenConditionalInstallsNoDependencies is true).
optionSelectedValue	string	'OPTION_SELECTED'	String used for the flag value of option dependencies.
parseOptionFlags	boolean or 'loose'	true	Whether to attempt to determine if a flag is an option flag to the best of our knowledge. If 'loose' is provided, we'll accept any flag name or value so long as it's only set by one option.

Examples

Parsing an Existing Installer

In Node, here's how you might go about parsing an existing Fomod installer:

import { parseInfoDoc, parseModuleDoc } from 'fomod';
import { JSDOM } from 'jsdom';
import fs from 'fs/promises';

// You can use whatever config you'd like
declare const config: FomodDocumentConfig;

// ModuleConfig.xml

const moduleText = await fs.readFile('path/to/ModuleConfig.xml');
const moduleDoc = new JSDOM(moduleText, {contentType: 'text/xml'});
const installer = parseModuleDoc(moduleDoc.window.document, config)

// Info.xml

const infoText = await fs.readFile('path/to/Info.xml');
const infoDoc = new JSDOM(infoText, {contentType: 'text/xml'});
const metadata = parseInfoDoc(infoDoc.window.document, config)

Or, for a more optimized example:

import { parseInfoDoc, parseModuleDoc } from 'fomod';
import { JSDOM } from 'jsdom';

declare const config: FomodDocumentConfig;

const [installer, metadata] = Promise.all([
    JSDOM.fromFile('path/to/ModuleConfig.xml').then((dom) => parseModuleDoc(dom.window.document, config)),
    JSDOM.fromFile('path/to/Info.xml').then((dom) => parseInfoDoc(dom.window.document, config)),
]);

Creating a New Installer

Creating a brand-new installer with this library is a breeze—you don't even need a document yet! Here's a quick example:

import { Fomod, FomodInfo, Step, SortingOrder, Group, GroupBehaviorType, Option } from 'fomod';

// ModuleConfig.xml

const module = new Fomod(`Superfluous and Obnoxious Snow`);

const onlyStep = new Step(`Superfluous and Obnoxious Snow`, SortingOrder.Explicit);
module.steps.add(onlyStep);

const snowColor = new Group('Snow Color', GroupBehaviorType.SelectExactlyOne);
onlyStep.groups.add(snowColor);

const snowColorWhite = new Option('White', 'Snow will be wonderfully white', 'fomod/images/snow_color/white.png');
snowColor.options.add(snowColorWhite);
const snowColorBlue = new Option('Blue', 'Snow will be blindly blue', 'fomod/images/snow_color/blue.png');
snowColor.options.add(snowColorBlue);
const snowColorRed = new Option('Red', 'Snow will be ridiculously red', 'fomod/images/snow_color/red.png');
snowColor.options.add(snowColorRed);
const snowColorGreen = new Option('Green', 'Snow will be gloriously green', 'fomod/images/snow_color/green.png');
snowColor.options.add(snowColorGreen);

const snowAmount = new Group('Snow Amount', GroupBehaviorType.SelectExactlyOne);
onlyStep.groups.add(snowAmount);

const snowAmountLight = new Option('Light', 'Snow will be lightly laid', 'fomod/images/snow_amount/light.png');
snowAmount.options.add(snowAmountLight);
const snowAmountMedium = new Option('Medium', 'Snow will be moderately made', 'fomod/images/snow_amount/medium.png');
snowAmount.options.add(snowAmountMedium);
const snowAmountHeavy = new Option('Heavy', 'Snow will be heavily heaped', 'fomod/images/snow_amount/heavy.png');
snowAmount.options.add(snowAmountHeavy);
const snowAmountBlizzard = new Option('Blizzard', 'Snow will be blizzardly blustered', 'fomod/images/snow_amount/blizzard.png');
snowAmount.options.add(snowAmountBlizzard);

// Info.xml

const info = new FomodInfo({
    Name: 'Superfluous and Obnoxious Snow',
    Author: 'BellCube',
    Id: '8311',
    Version: '6.6.6',
    Website: 'https://bellcube.dev/mods/superfluous-and-obnoxious-snow'
});

Cleaning Up

When you're done with a document, you'll want to clean it up. Here's how:

import { Fomod } from 'fomod';

// you can refer to the previous examples for how you might get a Fomod instance
declare const moduleConfig: Fomod;
declare const config: FomodDocumentConfig;

const thatOneDocument = document.implementation.createDocument(null, null, null);

// Associate the document with the Fomod instance
console.log(moduleConfig.asElement(thatOneDocument, config));

// We're done with the document, so let's clean it up
moduleConfig.decommission(thatOneDocument);

Credits

Contributors

• BellCube - Lead developer

Real-World E2E Test Authors

• Czasior - Co-author and Fomod writer for JK's Interiors Patch Collection
• Legacy of the Dragonborn Patches (Official) team
• GGUNIT - Author of Lux and Lux Patch Hub
• AllstaRawR - Author of T.I.T.S. U.P. - The Biggest FOMOD Ever