Mod Creation/Essentials

First time writing a mod for Melvor Idle? Consider starting with the Mod Creation/Getting Started guide.

Creating a Mod

A mod in Melvor Idle is simply composed of two parts: metadata and resources.

The metadata is defined in your mod's mod.io profile page (name, version, previews, etc.) and in a manifest.json file that must be located at the root of your mod's directory (this holds metadata that tells the Mod Manager how to load your mod).

Resources are really everything else. JavaScript modules and scripts, CSS stylesheets, images, sounds, etc. are all considered resources that will be accessed through either the manifest or dynamically through your JavaScript code. When referencing a resource from anywhere (manifestor code), the path should always be relative to the root of your mod (where the manifest.json file is located).

The Manifest

Before you begin writing code, it's a good idea to start by defining some metadata in the manifest.json file. A complete manifest.json might look like the following:

{
  "namespace": "hello-world",
  "icon": "assets/icon.png",
  "setup": "src/setup.mjs",
  "load": ["assets/style.css"]
}

namespace?: string

A few important modding APIs (tools) available from JavaScript require a namespace to be defined. This helps the game to keep your mod's data organized - think of this as an id for your mod that will be used by other mods and the game itself to access stored data that you've defined. As such, it's best to choose a namespace that easily identifies your mod in case another mod wants to interact with it.

The namespace can only contain alphanumeric characters and underscores and cannot start with the word "melvor".

Namespace	Valid
helloWorld	✔️
hello_world_123	✔️
HelloWorld!	❌
melvorWorld	❌

While this property is optional, it's good practice to include it to avoid future troubleshooting if you end up using an API that requires a namespace.

icon?: string

An optional icon to be displayed alongside your mod in a number of places, like the My Mods list in the Mod Manager. The value should be the path to the image file relative to the root of your mod (where your manifest is located). Accepted file types for an icon are .png or .svg, and the icon is typically displayed at a maximum of 38px in-game.

setup?: string

This property is required only if the "load" property is not present in the manifest.

This value should be a file path pointing to a JavaScript module to act as the entry-point to your mod; this concept will be covered more in the following section.

load?: string | string[]

This property is required only if the "setup" property is not present in the manifest.

This value accepts either a single path or an array of paths to resources to load. These resources are loaded in the order of the array, after the "setup" resource has been run. Valid resources to be loaded through this property are JavaScript script files (.js), JavaScript module files (.mjs), CSS stylesheets (.css), and HTML files containing templates (.html). However, unless your mod is very simple, the recommended approach to loading JavaScript resources (.js or .mjs) is through code in your mod's entry-point ("setup").

It's also important to note that while .js is considered a valid extension for JavaScript module files for the "setup" property, modules loaded through "load" must end with .mjs or they will be treated as regular script files.

Structuring Your Code

Using Modules (Recommended)

There are a number of ways to structure your code to be loaded, whether it's scripts or modules, "setup" or "load". Each might have a good use case but the recommended approach for most mods is to write your code using JavaScript modules and to have a single entry-point (defined as "setup" in manifest.json), while leaving the "load" property exclusively for loading your CSS.

Using this approach will keep your code clean and manageable, while avoiding polluting the global JavaScript scope, and as a result, avoiding conflicts with other mods. If you're unfamiliar with JavaScript modules, you can check out resources like JavaScript Modules on W3Schools or on MDN for a more detailed look. The general pattern you'll be using is exporting module "features" (functions, variables, etc) and then import them into other modules for use. This is also the approach this guide will use in all of its examples.

Let's start with what a module that's defined as your mod's "setup" entry-point should look like:

// setup.mjs
export function setup(ctx) {
  console.log('Hello World!');
}

We export a function named setup here because that is what the Mod Manager looks for when loading a "setup" module. Without one, an error would be thrown when loading this mod. This setup function is called and receives the mod's context object as soon as the mod is loaded, which happens just before the character select screen is visible. Therefore, this mod would write 'Hello World!' to the console at that time.

To take advantage of the modular approach to JavaScript, however, we cannot use a static import at the top of the file like we would prefer to in a regular JavaScript environment. Due to the nature of how modding resources are stored, we have to dynamically import modules using a special loadModule function, contained within the context object. This acts identical to a dynamic import but allows you to use a resource path relative to the root of your mod.

If we define a helper module helper.mjs:

// helper.mjs
export function greet(name) {
  console.log(`Hello, ${name}!`);
}

We can then use code we export in our setup function:

// setup.mjs
export async function setup({ loadModule }) {
  const { greet } = await loadModule('helper.mjs');
  greet('Melvor'); // > Hello, Melvor!
}

If you need to access the context object from your helper module, there are two approaches:

1. Pass the context object from the setup function to the loaded module:

// configService.mjs
export function init(ctx) {
  // Perform actions using the context object here...
}

// setup.mjs
export async function setup(ctx) {
  const configService = await ctx.loadModule('configService.mjs');
  configService.init(ctx);
}

2. Use the getContext method on the global mod object:

// configService.mjs
const ctx = mod.getContext(import.meta);

export function init() {
  // Perform actions using the context object here...
}

You must pass import.meta - a special JavaScript object available in all modules - to the mod.getContext method to receive your mod's context object.

Using Scripts

If you choose to include plain scripts in your mod, whether it's out of familiarity or a special use case, you can load (inject) scripts into the game either through the context object (perhaps received from a "setup" module) or the "load" property of the manifest.

Loading a script through the context object is very similar to loading a module but you will not receive back a value.

export async function setup({ loadScript }) {
  // Make sure you await the call to loadScript if your code beyond relies on it
  await loadScript('hello-melvor-script.js');
  // hello-melvor-script.js has executed

  // But don't bother awaiting it if it's not time-sensitive
  loadScript('some-independent-script.js');
}

From inside your script, you can still access the context object:

mod.register(ctx => {
  // Use the context object here
});

Note that the mod.register method will only work on scripts injected through either loadScript or the "load" property of the manifest.

The Context Object

Your mod's context object is the central point used for setting up your mod and making modifications to the game. The majority of the other sections in this guide will cover the concepts enabled through the APIs available on the object. For a more in-depth look at the documentation for the context object, refer to the Mod Creation/Mod Context API Reference guide.

Accessing Your Mod's Resources

Chances are you will package some resources in your mod that aren't covered by the loading options defined in the manifest and instead need to rely on loading these resources through your code. Your mod's context object provides methods for retrieving these resources. Keep in mind that all file path references to your resources should be relative to the root of your mod. Some common scenarios are below.

Load (Import) a Module

Use ctx.loadModule to import a JavaScript module's exported features.

// my-module.mjs
export function greet(name) {
  console.log(`Hello, ${name}!`);
}

export const importantData = ['e', 'r', 'e', 'h', 't', ' ', 'o', 'l', 'l', 'e', 'h'];

// setup.mjs
export async function setup({ loadModule }) {
  const myModule = await loadModule('my-module.mjs');
  myModule.greet('Melvor'); // Hello, Melvor!
  console.log(myModule.importantData.reverse().join('')); // hello there
}

Load (Inject) a Script

Use ctx.loadScript to inject a JavaScript file into the page.

// setup.mjs
export await function setup({ loadScript }) {
  // Wait for script to run
  await loadScript('my-script.js');
  // Or not
  loadScript('my-independent-script.js');
}

Load (Inject) HTML Templates

Use ctx.loadTemplates to inject all <template> elements into the document body.

// setup.mjs
export function setup({ loadTemplates }) {
  loadTemplates('my-templates.html');
}

Load (Inject) a Stylesheet

Use ctx.loadStylesheet to inject a CSS file into the page.

// setup.mjs
export function setup({ loadStylesheet }) {
  loadStylesheet('my-styles.css');
}

Load Data from JSON

Use ctx.loadData to read and automatically parse a JSON resource.

// my-data.json
{
  "coolThings": [
    "rocks"
  ]
}
// setup.mjs
export async function setup({ loadData }) {
  const data = await loadData('my-data.json');
  console.log(data.coolThings[0]); // ['rocks'] 
}

Images, Sounds, and Anything Else

Nearly any resource can be accessed and used in some way with ctx.getResourceUrl - the helper methods above all use this behind the scenes. With the resource's URL, you can use built-in JavaScript methods to consume the resource.

// setup.mjs
export function setup({ getResourceUrl }) {
  const url = getResourceUrl('sea-shanty-2.ogg');
  const song = new Audio(url);
  song.loop = true;
  song.play();
}

Game Lifecycle Hooks

Utilizing the game's lifecycle hooks will allow your mod to perform actions at specific times, which may be useful for waiting for certain game objects to be available. The game lifecycle hooks are as follows:

• onModsLoaded: Occurs after all enabled mods have completed their initial load
• onCharacterSelectionLoaded: Occurs after the character selection screen is completely loaded.
• onCharacterLoaded: Occurs after a character has been selected and all game objects have been constructed, but before offline progress has been calculated.
• onInterfaceReady: Occurs after offline progress has been calculated and the in-game interface can be reliably modified. Also useful for any long-running, or non-vital processes that might negatively impact the player experience by increased character load times.

All of the game's lifecycle hooks are available through your mod's context object and accept a callback function as a sole parameter. This callback function can be synchronous or asynchronous and will be executed at the specified time and receive your mod's context object as a parameter.

// setup.mjs
export function setup({ onModsLoaded, onCharacterLoaded, onInterfaceReady }) {
  onModsLoaded(ctx => {
    // Utilize other mod APIs at character select
  });

  onCharacterSelectionLoaded(ctx => {
    // Build or modify character selection UI elements
  });

  onCharacterLoaded(ctx => {
    // Modify or hook into game objects to influence offline calculations
  });

  onInterfaceReady(ctx => {
    // Build or modify in-game UI elements
  });
}

Mod Settings

Your mod can define settings for the player to interact with and visually configure your mod in-game. This feature is accessible through a settings property on the context object. If your mod has any settings defined, your mod will appear in the sidebar under Mod Settings. Clicking this will open up a window with all of your defined settings.

Settings' values are persisted on a per-character basis and will be saved within the character's save file.

Settings are divided (in code and visually) into sections. Get or create a section using the section(name) method on the settings object. The value passed in for the name parameter is used as a header for the section, so this should be human-readable. These sections are displayed in the order that they are created.

// setup.mjs
export function setup({ settings }) {
  // Creates a section labeled "General"
  settings.section('General');

  // Future calls to that section will not create a new "General" section, but instead return the already existing one
  settings.section('General');
}

The object returned from using section() can then be used for adding settings to that section. Refer to the next section for settings configurations.

// setup.mjs
export function setup({ settings }) {
  const generalSettings = settings.section('General');
  // You can add settings one-by-one
  generalSettings.add({
    type: 'switch',
    name: 'awesomeness-detection',
    label: 'Awesomeness Detection',
    hint: 'Determines if you are awesome or not.',
    default: false
  });

  // Or multiple at a time by passing in an array
  generalSettings.add([{
    type: 'label',
    display: 'I am just a label though my story seldom told...'
  }, {
    type: 'number',
    name: 'pick-a-number',
    label: 'Pick a Number',
    hint: '1 through 10'
  }]);
}

You can then get or set the value of any defined setting by its name property.

// elsewhere.mjs
const { settings } = mod.getContext(import.meta);

const generalSettings = settings.section('General');
generalSettings.set('pick-a-number', 1);
console.log(generalSettings.get('pick-a-number')); // 1

Setting Types

There are currently eight predefined setting types that will automatically create a usable input:

• Text
• Number
• Switch
• Dropdown
• Button
• Checkbox Group
• Radio Group
• Label

In addition, you add a custom setting by configuring additional properties. For more information on the configuration options available for each of these, refer to the relevant section of the Mod Creation/Mod Context API Reference guide.

Customizing the Sidebar

If you want to add or modify the in-game sidebar (the menu with the bank, skills, etc.) there is an globally-scoped in-game API, sidebar, for doing so. The sidebar is organized into four levels:

• Sidebar
  • Categories
    • Items
      • Subitems

An example of a category is Combat and Attack would be an item within that category. Subitems are what's used for the Completion Log's sections.

Each of the customizable (categories, items, subitems) pieces are generally interacted with the same way.

const combat = sidebar.catetory('Combat'); // Get the Combat category, or create one if it doesn't exist
const attack = sidebar.category('Combat').item('Attack'); // Get the Attack item within Combat or create one if it doesn't exist
attack.subitem('Wut'); // Get the Wut subitem within Attack or create one if it doesn't exist

In addition, these can be called with a configuration object as a second parameter to create or update the existing piece with the new configuration.

sidebar.category('Combat').item('Slayer', {
  before: 'Attack', // Move the Slayer item above Attack
  ignoreToggle: true // Keep Slayer visible when its category has been hidden
});

The full definition of each sidebar piece's configuration object can be found in the Mod Creation/Sidebar API Reference guide.

If you need to retrieve all existing categories, items, or subitems, use their respective methods:

sidebar.categories(); // returns an array of all categories
sidebar.category('Combat').items(); // returns an array of all Combat items
sidebar.category('General').item('Completion Log').subitems(); // returns an array of all Completion Log subitems

Removing categories, items, and subitems is also possible:

sidebar.category('Non-Combat').remove(); // Remove the entire Non-Combat category
sidebar.removeCategory('Combat'); // Alternative (this avoids creating a Combat category if it didn't already exist)
sidebar.removeAllCategories(); // Remove all categories, but why?

// Same kind of structure for items and subitems:
sidebar.category('Modding').item('Mod Manager').remove();
sidebar.category('General').item('Completion Log').removeAllSubitems();

You can find specifics about the sidebar API in the Mod Creation/Sidebar API Reference guide.

Storing Data

There are two options for storing data for your mod that isn't already saved as part of the game or settings: data saved with a character or data saved to the player's account. For most cases, however, character storage should be the preferred location and account storage used sparingly. Both of these stores are available through your mod's context object, as characterStorage and accountStorage, respectively. Aside from where the data is ultimately saved, character and account storage have identical methods and behaviors. Character storage is not available until after a character has been loaded (onCharacterLoaded lifecycle hook).

// setup.mjs
export function setup({ characterStorage }) {
  // This would all function identically with accountStorage, but also be available across characters
  characterStorage.setItem('my-favorite-pet', 7);

  console.log(PETS[characterStorage.getItem('my-favorite-pet')].name); // Larry, the Lonely Lizard

  characterStorage.removeItem('my-favorite-pet');

  characterStorage.clear(); // Removes all currently stored items
}

Limitations

Currently, a mod's character storage and account storage are each (separately) limited to 8,192 bytes (8kb) of total data. This means each character can store up to 8kb per mod, but only 8kb total can be stored to an account.

In addition, only JSON-serializable data can be stored. This includes any JavaScript primitive value (strings, numbers, and booleans) or an object or array containing only primitive values (or an object or array containing only primitive values, etc.). You do not have to serialize/deserialize the data yourself.

Finally, due to the nature of account data being persisted to the cloud, data integrity cannot be 100% guaranteed due to possible network issues the player might experience.

Game Object Patching/Hooking

A common modding scenario is to want to override/modify an in-game method or perform an action before or after it has completed. Your mod's context object contains a patch property that can be used for this these cases. Patches can only be applied to methods that exist on a JavaScript class (Player, Enemy, CombatManager, Woodcutting, etc.). To start, define the class and method that you want to patch:

// setup.mjs
export function setup({ patch }) {
  const xpPatch = patch(Skill, 'addXP');
}

From there you can use that patch to perform any of the following actions.

Do Something Before

Use the before method on the patch object to execute code immediately before the patched method. In addition, the callback hook will receive the arguments that were used to call the patched method as parameters, and can optionally modify them by returning the new arguments as an array.

// setup.mjs
export function setup({ patch }) {
  patch(Skill, 'addXP').before((amount, masteryAction) => {
    console.log(`Doubling XP from ${amount} to ${amount * 2}!`);
    return [amount * 2, masteryAction]; // Double all XP gains
  });
}

Do Something After

Use the after method on the patch object to execute code immediately after the patched method. In addition, the callback hook will receive the value returned from the patched method along with the arguments used to call it as parameters. Optionally, an after hook can choose to override the returned value by returning a value itself. Only a return value of undefined will be ignored.

// setup.mjs
export function setup({ patch }) {
  patch(Player, 'rollToHit').after((willHit) => {
    if (!willHit) console.log('A miss? I think not!');
    return true;
  });
}

Replace the Method Entirely

The replace method on the patch object will override the patched method's body, but before and after hooks will still be executed. The replacement method will receive the current method implementation (the one being replaced) along with the arguments used to call it as parameters. The return value of the replacement method will be the return value of the method call, subject to any changes made in an after hook.

// setup.mjs
export function setup({ patch }) {
  patch(Skill, 'addXP').replace(function(o, amount, masteryAction) {
    // Prevent any woodcutting XP  
    if (this.id === 'melvorD:Woodcutting') return;

    // Double any mining XP
    if (this.id=== 'melvorD:Mining') return o(amount * 2, masteryAction);

    // Grant all other XP as normal
    return o(amount, masteryAction);
  });
}

It's important to note that the using the replace method replaces the current method implementation. This means that multiple replacements on the same patched method will be executed in reverse order than they were declared:

// setup.mjs
export function setup({ patch, onInterfaceReady }) {
  const xpPatch = patch(Skill, 'addXP');

  xpPatch.replace(xpA);
  xpPatch.replace(xpB);

  onInterfaceReady(() => {
    game.woodcutting.addXP(100);
    // Logs:
    // XP replace B
    // XP replace A
  });
}

function xpA(o, amount, masteryAction) {
  console.log('XP replace A');
  return o(amount, masteryAction);
}

function xpB(o, amount, masteryAction) {
  console.log('XP replace B');
  return o(amount, masteryAction);
}

Exposing APIs

If your mod serves as a tool for other mods to integrate with, exposing APIs through the context object using ctx.api is the recommended approach. This is especially useful when paired with a mod developed using modules. The api method accepts an object and will expose any properties on that object to the global mod object within the api['your-mods-namespace'] property. You can call the api method multiple times to append more APIs.

// manifest.json
{
  "namespace": "helloWorld",
  "setup": "setup.mjs"
}
// setup.mjs
export function setup({ api }) {
  api({
    greet: name => console.log(`Hello, ${name!}`);
  });
}

Other mods would then be able to interact with your API:

// some other mod
mod.api.helloWorld.greet('Melvor'); // Hello, Melvor!

The Dev Context

To make it easier to test code before committing to uploading a mod, there is a 'dev' mod context that you can access to try out any of the context object's methods that don't require additional resources, i.e. you can't use loadModule. To access this context, you can use the following in your browser console:

const devCtx = mod.getDevContext();

This method/context should not be used from within a mod.

Next Steps

Hopefully this guide covers most common modding scenarios and will be a useful reference during your mod development time. For more in-depth looks at specific concepts, consider checking out the following guides:

• Mod Creation/Mod Context API Reference
• Mod Creation/Sidebar API Reference