Extracts sections of uuids and transforms them into properties on vanilla object for use in games, simulations, and tests.

uuid, random, generator, mock, simulation, test data
bower install ephemera


EphemeraJS Build Status

A library for converting random uuid strings into full bodied objects. Intended applications include games, tests, and simulations. The library is intended to make it possible to configure random but realistic data within ranges by extracting sections of a uuid then transforming that section into a property according to predetermined rules. The system is pluggable so that you can create your own custom transformations.

An Example

var e = require('ephemera'),
	uuid = require('node-uuid'),
	i = 0,
	names = ['Mike', 'John', 'Steve'],
    Person = e.objectFactory(),
    people = [];

    .addProperty('age', [0,4], e.int(18,65));
    .addProperty('weight', [0,4], e.float(100,250));
    .addProperty('name', [2,16], e.arr(names));

for (; i<4; i++) {


At the end of this script, an array of 4 objects will be logged to the console something like this:

    age: 35,
    weight: 182.35909,
    name: "Steve"
    age: 27,
    weight: 174.69832,
    name: "Mike"
    age: 62,
    weight: 229.50807,
    name: "John"
    age: 54,
    weight: 102.18436,
    name: "Steve"


The ephemera object exposes an objectFactory method which returns a constructor function which you will eventually use to create your objects. You'll want to add several properties to the constructor first though.

Use the addProperty() method of your objectFactory to define a custom property. The first parameter defines the name of the property you wish to create (ex: "name" in the example above). The second property is a two element array which contains the start and end positions in the UUID to reference when generating this property. The last property is a callback function that will transform the given portion of the UUID using whatever rules you wish.

Ephemera comes pre-baked with several convenient transformation methods. Each of the following functions takes one or more parameters and returns a customized callback function that will execute the transformation:

  • int(min,max) - creates a callback function which returns an integer between min and max for a given value from a UUID.

  • float(min,max) - creates a callback function which returns a float between min and max for a given value from a UUID.

  • arr(items) - creates a callback function which selects an item from the array items.

  • wArr(items) - creates a callback function which selects an item from the array of objects. Each element of items is an object with freq and value properties. The freq property is a float between 0 and 1 stating the probability that this item is selected. Frequencies must add up to 1 altogether. If an item is selected, the value property will be returned. Ex:

    e.wArr([ {value:'Sara', freq:0.5}, {value:'Joanna', freq:0.3}, {value:'Henrietta', freq:0.2} ]);

    In the above example, Sara has a 50% chance of being returned by the callback function. Joanna has a 30% chance, and Henrietta has a 20% chance.

  • colorHex() - creates a callback which returns hexadecimal colors values.

  • colorHexRange(min,max) - creates a callback which returns hexadecimal colors values between min and max, where min and max are hex color codes (#000000 - #ffffff).

Custom Transformations

You can also define your own custom callback transformations. Transformation functions receive one float as the first parameter. Behind the scenes, ephemera converts the fragment of the UUID passed to the constructor into a floating point number between 0 and 1. The exact floating point value is determined by dividing the actual hex value by the maximum possible hex value. Ex:

var uuid = '10ec58a-a0f2-4ac4-8393-c866d813b8d1',
    e = require('ephemera'),
    Person = e.objectFactory(),

Person.addProperty('age', [0,2], function(float) { return float; });
somebody = Person(uuid);

In the above code, Person() will remove any dashes from the UUID. Next, Person() will create properties for a new object. In this case, the only property is 'age'. Person will slice the UUID string using the [0,2] parameters. Person() looks at the length of the resulting string and determines the maximum possible hex value of the same length (ff). Then, Person() divides the UUID slice by the highest possible hex value. Since the string has length two, the highest possible hex value would be ff. So, the value passed to my custom callback will be 10/ff (or in decimal 16/255) which comes out to be 0.06274509803921569. This value is stored in the property age on someGuy, and then logged to the console at the end of the script.

Interrelated Properties

All transformation callbacks also receive a second parameter which is the current object as it's being generated. Built- in transformation functions simply ignore this second parameter (and so can you safely). However, you can also use the current object's pre-existing properties to make some properties dependent on the value of other properties. Example:

var uuid = '10ec58a-a0f2-4ac4-8393-c866d813b8d1',
    e = require('ephemera'),
    Person = e.objectFactory(),

    .addProperty('age', [0,2], e.int(6,95))
    .addProperty('job', [3,16], function(float, obj) {
        var jobs = ['lawyer','manager','teacher','doctor','ceo','macdonalds'],
            jobPicker = e.arr(jobs);

        if (obj.age > 65) {
            return 'retired';
        } elseif (obj.age < 22) {
            return 'student';
        } else {
            return jobPicker(float);
somebody = Person(uuid);

In the example code above, the job property is dependent on the age. Properties are added to objects in the order you add them to the constructor, so in our example above age is determined before job.