Undum 2 documentation

Javascript API


The character is created for you, but is passed into most of the functions that you define. It consists of an object with no methods and two properties:


The qualities object maps quality identifiers to their current value. Your code finds the current value associated with a quality by reading from this object, for example:

var gold = character.qualities.gold;

To set a quality, you have two choices. If you know the quality you want to set will not appear in the user interface, then you can set it directly:

character.qualities.gold += 1;

If it does appear on-screen, then this approach will mean that the character panel doesn't update, and the screen will be out of sync with the actual value. Instead it is better to use the System method setQuality, which also updates the UI:

system.setQuality('gold', character.qualities.gold+1);

It is fine to use setQuality if the quality isn't visible, making this the preferred option for all quality modifications.


Not every bit of data you want to associate with a character fits nicely into a quality. The sandbox is a general storage space for any further data you want to store in the course of your game, for example:


Sandbox data is never visible to the user, so you can use any data structures you like here, to any depth.


The system represents the interface between your code and the user-interface. You don't create your own System object, it is passed into your code.


Since version 2

Removes all content from the page, clearing the main content area.

Although Undum is designed to keep the flow of the narrative on one page, sometimes you do need to start a new page, and this allows you to do so.

The elementSelector is options. If you give it, then the DOM element matching the selector is cleared, rather than the whole document.

write(content, elementSelector)

Writes new content to the main flow of the story. The content you pass in must be either valid DOM elements already, or else be a string containing text in Display Content format.

The elementSelector is optional. If you provide it, then the new content will be added after the DOM element in the document that matches the selector. This allows you to do out-of-order addition of content. Simply add a paragraph with an id in your game, then later you can give this id as a selector to write, and the new content will be inserted immediately following that paragraph, regardless of how much extra content has been added since that point. If no selector is given then #content is used, i.e. the content is added at the end of the document. The writeBefore method inserts content at the start of the document, or before a selector.

The story will scroll to the start of the insertion point. If you do not wish to animate this scrolling, but just jump right there, you can switch off jQuery's animation system by adding jQuery.fx.off=true to your initialization code. This is particularly useful when debugging.

writeHeading(content, elementSelector)

Writes new content into the story and formats it as a heading. This method work exactly as write, but wraps the content you provide into a h1 html tag.

writeBefore(content, elementSelector)

Writes content into the story. This method is identical to write, above, except that the content is written at the start of the story, or if a selector is given, inserted before the matching element. On browsers that support it, the story will be scrolled to the insertion point.


Since version 2

Creates a standard block of choices, one for each of the given situation ids. The text used in the links will be whatever is returned by the situation's optionText method. In addition, if the situation's canChoose method returns false, then the option will be displayed, but will not be clickable.

getSituationIdChoices(listOfIdsOrTags, minChoices, maxChoices)

Since version 2

This function is a complex and powerful way of compiling implicit situation choices. You give it a list of situation ids and situation tags. Tags should be prefixed with a hash # to differentiate them from situation ids. The function then considers all matching situations in descending priority order, calling their canView functions and filtering out any that should not be shown, given the current state. Without additional parameters the function returns a list of the situation ids at the highest level of priority that has any valid results. So, for example, if a tag #places matches three situations, one with priority 2, and two with priority 3, and all of them can be viewed in the current context, then only the two with priority 3 will be returned. This allows you to have high-priority situations that trump any lower situations when they are valid, such as situations that force the player to go to one destination if the player is out of money, for example.

If a minChoices value is given, then the function will attempt to return at least that many results. If not enough results are available at the highest priority, then lower priorities will be considered in turn, until enough situations are found. In the example above, if we had a minChoices of three, then all three situations would be returned, even though they have different priorities. If you need to return all valid situations, regardless of their priorities, set minChoices to a large number, such as Number.MAX_VALUE, and leave maxChoices undefined.

If a maxChoices value is given, then the function will not return any more than the given number of results. If there are more than this number of results possible, then the highest priority resuls will be guaranteed to be returned, but the lowest priority group will have to fight it out for the remaining places. In this case, a random sample is chosen, taking into account the frequency of each situation. So a situation with a frequency of 100 will be chosen 100 times more often than a situation with a frequency of 1, if there is one space available. Often these frequencies have to be taken as a guideline, and the actual probabilities will only be approximate. Consider three situations with frequencies of 1, 1, 100, competing for two spaces. The 100-frequency situation will be chosen almost every time, but for the other space, one of the 1-frequency situations must be chosen. So the actual probabilities will be roughly 50%, 50%, 100%. When selecting more than one result, frequencies can only be a guide.

Before this function returns its result, it sorts the situations in increasing order of their displayOrder properties.


Carries out the action associated with the given URL, as if it had been the href of a HTML link that the user clicked. This allows you to procedurally change situation and carry out actions from your code.


This holds a general purpose random number generator. It is an object derived from the Random prototype, so see Random below for details on its API.


This is a numeric value holding the current time, in seconds, since the player began playing the game. This value is correctly propagated across saves, so it is the only way you should track timing. In particular you should never call new Date() and use that value to determine the outcome of any event. You can use the current date to display the current date, for example, but not to control what actions or situations are available. See the section on Loading and Saving for more details of why this is important.

setQuality(qualityId, newValue)

Sets the character's given quality to the given value. This function also updates the character panel, animating the change in value if that is necessary. Do not directly set quality values in the character, because the user-interface will not detect and reflect those changes.

animateQuality(qualityId, newValue, options)

Like setQuality, this function changes the current value of the given quality. In addition, however, it displays a progress bar that shows to the user how the value has changed. The options parameter should be an object containing options for how the bar should display. The available options are:

  • from: The proportion along the progress bar where the animation starts. Defaults to 0, valid range is 0-1.

  • to: The proportion along the progress bar where the animation ends. Defaults to 1, valid range is 0-1.

  • showValue: If true (the default) then the new value of the quality is displayed above the progress bar.

  • displayValue: If this is given, and showValue is true, then the given value is used above the progress bar. If this isn't given, and showValue is true, then the display value will be calculated from the QualityDefinition, as normal. This option is useful for qualities that don't have a definition, because they don't normally appear in the UI.

  • title: The title of the progress bar. If this is not given, then the title of the quality is used. As for displayValue this is primarily used when the progress bar doesn't have a QualityDefinition, and therefore doesn't have a title.

  • leftLabel, rightLabel: Underneath the progress bar you can place two labels at the left and right extent of the track. These can help to give scale to the bar. So if the bar signifies going from 10.2 to 10.5, you might label the left and right extents with "10" and "11" respectively and have the from and to value be 0.2 and 0.5 respectively. If these are not given, then the labels will be omitted.


Sets the block of character text that appears in the character panel. As for the write method, this text should be either valid DOM elements, or a string meeting the Display Content requirements.


Call this function with an Undum link URL (e.g. ballroom, or ballroom/open-cabinet). It will remove all occurrences of that link from the page. This is equivalent to what happens when you change situation, or when you click a link marked with the once CSS class. It allows you to control what options are available dynamically, from your code.


The Random object provides a set of tools for simple random number generation, in a way that is guaranteed to work with the Loading and Saving functionality in Undum. An instance of Random is provided in the rnd property of the System object, so you will never need to create your own. It has the following methods:


Generates a random number between 0 and 1, where 0 is inclusive, and 1 is exclusive. You can use this to check against known probabilities, such as:

if (system.rnd.random() > 0.5) {

To check for a 50/50 chance.

randomInt(min, max)

Return a random number between the given two values, where both values are inclusive. So randomInt(2,3) generates either 2 or 3.

dice(n, dx, plus)

Rolls n dice with dx sides and adds plus to the result. This allows you to easily get results for rolls from regular RPG-style games, such as 3d6+2. The plus parameter may be negative or positive.

aveDice(n, plus)

Rolls n averaging dice, and adds plus to the result. Averaging dice are a special type of d6 with sides marked [2,3,3,4,4,5]. They represent the fact that most people are fairly average, and results should not lie at the extremes.


Rolls dice according to the given definition string. The string should be of the form xdy+z, where the x component and z component are optional. This rolls x dice of with y sides, and adds z to the result, the z component can also be negative: xdy-z. The y component can be either a number of sides, or can be the special values 'F', for a fudge die (with 3 sides, +,0,-), '%' for a 100 sided die, or 'A' for an averaging die (with sides 2,3,3,4,4,5).


The Situation object is the prototype of all the situations in your game. It can be used directly, or through its more common derived type, SimpleSituation. The base Situation gives you maximum flexibility, but SimpleSituation provides more functionality and can produce terser code.

new Situation(options)

Creates a new situation. The options array can specify your implementation for any or all of the following methods of this class:

  • enter
  • exit
  • act
  • optionText
  • canView
  • canChoose

(see below for explanations of those methods). This allows you to easily create situations that override certain behaviors with code such as:

    enter: function(character, system, from) {
        ... your implementation ...

without having to subclass Situation to provide your own implementations.

In addition the following options can be passed in.

  • tags: A list of tags with which to label this situation. These are primarily used to generate implicit lists of choices with System.getSituationIdChoices. Tags are arbitrary strings. You can pass a list of strings, or a single string. If you pass a single string, it will be split at spaces, commas and tabs to form a list of tags. For this reason, tags normally do not contain spaces, commas or tabs (though if you pass in a list, and don't expect Undum to do the splitting for you, you can include any characters you like in a tag).

  • optionText (as a string): If given as a string, rather than a function, this text will be returned whenever optionText(...) is called.

  • displayOrder: A numeric value, defaults to 1. When displaying lists of implicitly generated choices, the options be displayed in increasing value of this parameter.

  • priority: Can be any number, defaults to 1. When generating lists of choices implicitly, situations are considered in descending priority order. If higher priority situations can be displayed, lower priority situations will be hidden. See System.getSituationIdChoices for details of the algorithm.

  • frequency: Any number, defaults to 1. When generating lists of implicit choices, where there are more choices available that slots to display them, situations will be chosen randomly, with a probability based on this value. See System.getSituationIdChoices for details of the algorithm.

enter(character, system, from)

This is called when Undum enters a situation. The character and system are instances of Character and System as described above. The from parameter is a string containing the situation identifier for the situation that we're arriving from.

This method is the most commonly overridden. It is commonly used to describe the current situation (by sending content to system.write()) and to update the character (by calling system.setQuality() or by changing data in the character's sandbox object)..

exit(character, system, to)

This method takes the same character and system parameters as enter. Its third parameter, to, is a string containing the identifier of the situation we're exiting to.

act(character, system, action)

This method again takes the same character and system parameters as before. Its third parameter is a string containing the action identifier corresponding to the link the player clicked. It is common to use an if statement or a switch to query this action identifier and decide what to do accordingly. For situations in which many different actions are possible, consider using the SimpleSituation prototype, which provides this switching behavior for you.

optionText(character, system, hostSituation)

This method is called by System.writeChoices to generate a label for links to this situation. The hostSituation is the situation that has asked for the choices to be displayed.

canView(character, system, hostSituation)

This method is called by System.getSituationIdChoices to determine whether this situation can be part of a list of choices in the current game state. It should return true or false.

canChoose(character, system, hostSituation)

This method is called by System.writeChoices to determine whether a link should be added to allow the user to enter this situation. If not, the choice will still appear, but will not be clickable.


This prototype builds on the basic Situation, providing tools to make it easy to output content in the enter method, and to switch between different functions depending on the action identifier passed into the act method. The exit method of SimpleSituation is exactly as for the base type Situation.

new SimpleSituation(content, options)

Creates a new simple situation that will display the given content when its enter method is called. The given options dictionary provides further control of the behavior of this type. Valid options are:

  • enter: Providing an enter function in the options parameter allows you to add additional behavior to the enter method. Your custom function will be called in addition to and after the default content is written to the screen. You cannot override SimpleSituation's enter method by providing this function. To override the method, you would have to create a derived type. If you provide an enter function, it should have the same form as Situation.enter.

  • act: Pass in a function to add additional behavior to the act method. As for enter, your method is called in addition to and after the built-in functionality.

  • exit: Because SimpleSituation has no default behavior for exit, any function you pass in here will be the only exit behavior for the object you are creating.

  • heading: The content that you specify will be written out verbatim. You can include headings in this content. Often it is more convenient to pass in just the text in the content parameter. In that case you may define this heading parameter to display a heading before the text. Unlike content, this doesn't need to conform to the Display Content requirements.

  • actions: This should be an object that maps action identifiers to responses. A response should be either some Display Content to write to the screen, or a function that will process that request. These functions should have the same signature as the Situation.act method. Each function will only be called if the situation receives a call to act with its corresponding identifier. This allows you to simply define functions that only get called when particular actions happen.

  • choices: An optional list of tags and situation-ids, with tags prefixed by a has symbol to distinguish them from situation ids. If given, this will cause the SimpleSituation to output an implicit block of choices after the content.

  • minChoices: If you have given a choices definition, you can set this to an integer value to change the number of choices that will appear. See System.getSituationIdChoices for more information on how this affects the output.

  • maxChoices: If you have given a choices definition, you can set this to an integer value to change the number of choices that will appear. See System.getSituationIdChoices for more information on how this affects the output.

An example SimpleSituation definition might be:

new SimpleSituation(
        heading: "Title",
        actions: {
            listen: function(character, system, action) {
                if (character.qualities.hearing > 5) {
                    system.write("<p>You hear a tinkling inside.</p>");
                } else {
                    system.write("<p>You hear nothing.</p>");
            search: "<p>You find nothing.</p>"

notice how the listen function is responsible for its own output, where the search property is a string in Display Content format, ready for output.

Functions in SimpleSituation

Both the content and the heading of a simple situation can be provided either as plain text, or as a function. If you provide a function, then it will be called with no arguments, and it should return a string to use for the output. This enables SimpleSituation to be used with other formatting and templating systems.


Quality definitions tell Undum how and where to display a quality in the character panel. Each quality definition has one method, format, which is responsible for converting a numeric quality value into a displayable quantity.

You define your qualities in your undum.game.qualities property.

new QualityDefinition(title, options)

Creates a new QualityDefinition. It is rare to call this constructor yourself, most often one of the derived types of QualityDefinition are used. They are defined below.

The title should be a string, and can contain HTML. It is used to label the quality in the character panel. It can be any string, it doesn't have to be in Display Content format.

Options are passed in in the options parameter. The following options are available.

  • priority: A string used to sort qualities within their groups. When the system displays a list of qualities they will be sorted by this string. If you don't give a priority, then the title will be used, so you'll get alphabetic order. Normally you either don't give a priority, or else use a priority string containing 0-padded numbers (e.g. "00001").

  • group: The identifier of a group in which to display this parameter. If a group is given, then it must be defined in your undum.game.qualityGroups property.

  • extraClasses: These classes will be attached to the <div> tag that surrounds the quality when it is displayed. A common use for this is to add icons representing the quality. In your CSS define a class for each icon, then pass those classes into the appropriate quality definitions.

format(character, value)

This is called by Undum to get a human readable string representing the given quality value for the given character. The method may return an empty string if the value has no need to be displayed, or it may return null if the quantity itself shouldn't be displayed. The difference here is significant. If your QualityDefinition returns the empty string, then the quality will appear in the character panel, but it will have no value marked. If it returns null, then it will be removed from the character panel entirely.

Most commonly the character parameter is ignored, but in your own derived types you can take advantage of being able to access other information about the character.

You may call this function yourself, but there is commonly no need. It will be called by Undum any time the corresponding quality needs to be displayed.


This is a derived type of QualityDefinition that displays the quality value by rounding it down to the nearest integer. This is ideal for most numeric statistics.


This is a derived type of IntegerQuality that only displays its value when it is non-zero. If it is non-zero then it formats in the same way as IntegerQuality. Whereas IntegerQuality whould show zero values as '0', this type of quality displays nothing.


This is a derived type of QualityDefinition that displays the quality value directly, as a full floating point value.


Sometimes you want qualities displayed in words rather than numbers. This is a derived type of QualityDefinition that allows you to define words corresponding to possible quality values.

new WordScaleQuality(title, words, options)

The title parameter is exactly as for QualityDefinition.

The words parameter determines what words will be used. It should be an array of strings. By default the first string will be used to represent a value of zero (after rounding down), and the second string a value of 1, and so on to the end of the array. Values outside the array are treated differently depending on the value of useBonuses in the options parameter.

The options parameter supports the same three options as QualityDefinition. It also takes the following additional parameters:

  • offset: With offset=0 (the default), a quantity value of 0 will map to the first word, and so on. If offset is non-zero then the value given will correspond to the first word in the list. So if offset=4, then the first word in the list will be used for value=4, the second for value=5. You can specify a non-integer offset value, in this case the offset is applied before the value is rounded down.

  • useBonuses: If this is true (the default), then values outside the range of words will be constructed from the word and a numeric bonus. So with offset=0 and five words, the last of which is 'amazing', a score of six would give 'amazing+1'. if this is false, then the bonus would be omitted, so anything beyond 'amazing' is still 'amazing'.


This is a derived type of WordScaleQuality that doesn't require you to specify the words you wish to use. It uses the word scale from the Fudge RPG: "terrible", "poor", "mediocre", "fair", "good", "great" and "superb".

new FudgeAdjectivesQuality(title, options)

The parameters title and options are as for the WordScaleQuality constructor. The offset option defaults to -3, however (in WordScaleQuality it defaults to 0), making "fair" the display value for 0.


An OnOffQuality returns null from its format method (i.e. removes itself from the character panel) when the corresponding quality value is zero. Otherwise it returns the empty string (i.e. it is shown in the panel, but doesn't have a value label). See QualityDisplay.format above for more details on this distinction.

new OnOffQuality(title, options)

The constructor for this type is the same as for QualityDefinition from which it is derived. It accepts one extra option:

  • onDisplay: If given, then rather than displaying the empty string, it displays the given string when its corresponding value is non-zero. This can be used to display a check-mark, for example ({onDisplay:"&#10003;"}), or even a HTML img tag.


A YesNoQuality displays one of two strings depending whether its value is zero or not.

new YesNoQuality(title, options)

The constructor for this type is the same as for QualityDefinition from which it is derived. It accepts two extra options:

  • yesDisplay, noDisplay: Either or both of these may be given. If they are given, then they should be set to a string, which will be used to indicate non-zero or zero values, respectively. By default "yes" and "no" are used.


A quality group defines a set of qualities that should be displayed together in the character panel, under an optional subheading. You could use quality groups to distinguish between qualities representing a character's innate abilities and their equipment, for example.

You define your quality groups in your undum.game.qualityGroups property.

new QualityGroup(title, options)

Constructs a new quality group that will have the given title for a subheading. The title may be null, indicating that this group does not need a heading.

The options parameter should be an object with the given optional parameters:

  • priority: A string used to sort quality groups. When the system displays more than one quality group, they will be sorted by this string. If you don't give a priority, then the title will be used, so you'll get alphabetic order. Normally you either don't give a priority, or else use a priority string containing 0-padded numbers (e.g. "00001").

  • extraClasses: These classes will be attached to the <div> tag that surrounds the entire quality group when it is displayed. You can use this in addition to your CSS to radically change the way certain qualities are displayed.