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lordnull / dice.js

Generic RPG dice string parser and roller
MIT License
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dice.js

A Generic Dice syntax parser and evaluator for javascript.

This tool is oriented more for those who wish to implement game systems or character management systems. This means the read me can be a bit difficult to follow you're not a coder. However, the usage section should be enough to allow an end user to write useful rolling strings.

Dependency

Node's npm can be used to fetch the build and test dependencies. There are no run-time dependencies.

Build

An already built version for use in browsers is included under build; if you build manually, this will be overwritten.

To do a build that generates both uncompressed and minified versions, simply use make. 'make compile' only generates the uncompressed version. Both versions are placed in './build'.

Simply include either dice.js or dice.min.js in a script tag, and you're off.

For use with node and installed with npm, you should only need to do the usual var dice = require("./src/dice.js");.

Testing

Tests are run using jasmine. To do a single test run for both the browser, use make test. To run only browser tests, use make browser_test. To run only the node tests, use make node_test. To leave a browser used for testing running for debugging purposes, use make dbgtest. Jasmine will tell you what page you need to browse to the test to actually run; but by default it's http://localhost:8888.

Usage

Dice.js is a tool to roll dice and fill in certain values based on a given scope. In short:

var res = dice.roll(diceString, scopeObject);
console.log(+res);
console.log(dice.stringify(res));

The res is a number that can be used like any other. It has operations attached which allow it to be examined to determine how the total was achieved (thus why it is coerced into a primitive when logged above). The easiest way to analyze it is to have dice.js stringify it.

The diceString uses a simple-ish syntax to specify what dice to roll, how to roll them, and the sum of the rolls. While each individual part is simple, presenting it all at once can be overwhelming.

Basic Rolls

If you familiar with Dungeons and Dragons, the following should be familiar:

1d20 + 10

That is a valid statement for a dice roll. The 'd' separator is case insensitive:

1D20 + 10

You could simplify it a bit, in fact:

d20 + 10
D20 + 10

There are times when you would need to roll multiple sets of dice:

3d6 + d8 + 5

Or maybe you have a penalty:

d20 - 5

In some systems, there may be a minimum for the roll; in DnD, some weapons allow one to re-roll all ones:

3d2..6

This can be combined with the above statements:

3d2..6 + 5

For players of Fudge or Fate, negative numbers can be used for the minimum and maximum too, and in any order.

4d-1..1 + 1
4d1..-1 + 3

You may have noticed that in the Fudge examples, the -1 and 1 are reversed. This is because the numbers on either side of the .. are not a minimum and maximum, but a range. -1..1 and 1..-1 represent the same range. The DnD example of the minimum attack could be expressed as:

3d6..2

If you have played Star Wars d6, using a wild die is supported as well:

3d6 + 1w6
3D6 + 1W6

Using w instead of d means that die will be re-rolled and added to the result if it comes up as a the value to the right of the ... All the repeat rolls will show up as a single roll in the rolls property of the returned object.

Note that the xwn..m syntax will always reroll when the result is m. This means that 3w2..6 is not the same as 3w6..2. The former explodes the dice on a 6, while the latter explodes it on a 2.

Scopes

As you can see, the strings to define a roll are very similar to what players have been using for years with a minor addition to support minimum numbers. There is another feature, however, that makes this system even more powerful: scopes.

Let's take a very simplified DnD character, using only the ability modifiers:

var character = {
    name: 'Code Monkey',
    Strength: -2,
    Dexterity: -1,
    Constitution: 0,
    Charisma: 3,
    Wisdom: 3,
    Intelligence: 5
};

Using the rules above, we can write a roll for a strength check:

var roll = "d20 - 2";

Now if our character puts in effort to increase the stat:

character.Strength++;

Using the rules above we need to re-write the roll:

roll = "d20 - 1";

But what if we could just use the information in the character object? turns you, you can:

roll = "d20 + [Strength]";

When the roll is evaluated with the scope of the character, [Strength] is replaced with the Strength property of the character. The previous two examples are equivalent, with the bonus that if the character changes, new evaluations will use the updated properties.

dice.roll(roll, character);

The replacement works anywhere an integer can go:

3d8 + [Enhancement Bonus]d12
2d[Weapon Die]
3d2..[Weapon Die]
[Character Level]d6

Note how we allow spaces in the name. The only characters explicitly disallowed are [ and ].

If the scope contains values that are not integers, like 1.5, You can use one of the built-in rounding functions. Preface the variable box with f for round down (floor), c for round up (ceiling), or r for round to nearest.

1d20 + f[Half Level]

If the Half level was used without the f tag, an exception would be thrown.

For more advanced usage, scopes can be nested.

var scope = {
    'takes.priority': 3,
    'takes':{
        'priority': 5
    },
    'nested'{
        'value': 7
    }
};
var result = dice.roll("[takes.priority] + [nested.value]", scope);
result == 10; // because we look for an exact match of property name first

Sub-expressions

The Usual +, -, * and / are supported, with order of operations being observed: * and / done in order, then + and -.

If this is not desired, or you want to do some math where an integer would go, you can use a parenthesis expression. As with scopes, we can prepend them with the rounding flags f, c, and r. The rounding is required when using a sub-expression where an integer is expected.

For example, the half level from the scope example above could be re-written without needing an explicit half level on the scope.

1d20 + f([Level] / 2)

Or if you need to roll half your level in d6's:

c([Level] / 2)d6

Roll Modifiers

Many DnD players are familiar with the "4 dice, drop lowest" method of rolling character attributes. While this can be achieved in JavaScript with some code and inspecting the results, the goal is to allow many rolls to be written without needing to know how to code. This is where roll modifiers come in.

After any dice roll expression, you can add some rules to modify the result.

4d6{ drop lowest }
4d6{ keep highest 3 }
3d6{ reroll } // 3 dice, reroll 1's once.
3d6{ reroll <3 } // 3 dice, reroll 1's and 2's once.
3d6{ reroll 2x } // 3 dice, reroll 1's up to 2 times.
3d6{ reroll <3 2x } // 3 dice, reroll 1's and 2's up to 2 times.

Multiple modifiers can be used. Seperate them with a ;. They modifier the result of the rolls in the order by are listed.

4d6{ reroll ; drop lowest } // 4 dice, reroll 1's once, then drop lowest

Some modifiers also have a short form. When using the short form, only one modifier can be used.

4d6:dl // same as 4d6{ drop lowest }
4d6:k3 // same as 4d6{ keep highest 3 }

There are 4 modifiers: keep, drop, reroll, and explode. Each as a short form of some kind.

Keep

Keep a certain number of the highest or lowest of a roll.

'keep' which_type how_many

This also has several short forms, which are case-insensitive. Any of the short forms can have a number appended (no space before the number) to change it from a single die to that number. As usual, you can put a scope or rounded value in.

Drop

The inverse of keep, drop a number of the highest or lowest dice.

'drop' which_type how_many

This also has several short forms, which are case-insensitive. Any of the short forms can have a number appended (no space before the number) to change it from a single die to that number. As usual, you can put a scope or rounded value in.

Reroll

Given some condition, reroll dice a limited number of times. Note that unlimited re-rolling is not supported. If you need to always re-roll ones on a six-sided dice, just define d2..6.

'reroll' condition limit

A condition is a number (the comparitor) optionally preceded by any one of the following:

The condition is optional. If left out, it defaults to equal to the left value of a dice roll's range.

The limit is a number followed by the letter 'x'. The 'x' is there so we know it's always a limit. If the limit is omitted, it defaults to 1.

Reroll has a short form. :rr is the same as {reroll}.

Explode

Exploding dice a rolled again when certain number is rolled, with the new result being added to the result set (and thus total). When more than one die is rolled, any that meet the condition explode, and will continue until either the condition is not met, or the limit is met.

The long form is similar to reroll.

A condition is a number (the comparitor) optionally preceded by any one of the following:

The condition is optional. If left out, it defaults to equal to the right value of a dice roll's range.

The limit is a number followed by the letter 'x'. The 'x' is there so we know it's the limit. If the limit is omitted, it defaults to 10000.

There is a short form. Exploding dice were explained in the basic rolls section as using w instead of d; that's the short form. It is the same as using { explode =[max] } where [max] is the right side of the dice range.

Statistics

If you want some analysis for your rolls, you can get a result set created with some basic stats tagged in.

Using dice.statistics(rollString, scope, samples) returns an object:

    {
        'results': [dice_roll_result], // The result set generated
        'mean': number,                // The average of result set generated
        'min': number,                 // The smallest value in the result set
        'max': number,                 // The largest value in the result set
        'min_possible': number,        // The smallest value that could have
                                       // been generated.
        'max_possible': number,        // The largest value that could have
                                       // been generated.
    }

Currently the only roll modifiers considered during the statistics are the keep and drop modifiers.

Contributing

Fork and make a pull request with relevant tests. Opening issues is also welcome.