The Problem

Fabricator is based on the excellent Fabrication. Its purpose is to easily generate objects in JavaScript. It is particularly useful for testing.

Installation

npm install --dev @travelperksl/fabricator

Defining Models

Models are defined with Fabricator() in this way:

import { Fabricator, sequence } from '@travelperksl/fabricator'
import faker from 'faker'

const userFabricator = Fabricator({
  id: () => sequence('userId'),
  name: () => faker.name.firstName() + faker.name.lastName(),
  admin: false,
})

You simply pass a model definition. The definition is an object where each key is a function or a static value. If you need dynamic data you can use sequence() or use a library like faker.

You can also extend existing models. For example:

const adminFabricator = userFabricator.extend({ admin: true })

In this case, adminFabricator will inherit all the properties from userFabricator but will overwrite the value for the admin property.

Fabricating Objects

Once your model is defined you can create it by calling the returned function:

const user = userFabricator()
// => { id: 1, name: 'John Doe', admin: false }
const admin = adminFabricator()
// => { id: 2, name: 'Susan Smith', admin: true }

You can overwrite some values by passing a model definition as parameter:

const blockedUser = userFabricator({ isBlocked: true })
// => { id: 3, name: 'Donald Brown', admin: false, isBlocked: true }

Note that there's a difference between passing a function and a static value in a fabricator definition. A function gets executed every time you create a new object, a constant value is cached. Consider the following example:

const withConstant = Fabricator({ foo: Math.random() })
withConstant() // => { foo: 0.11134742452557367 }
withConstant() // => { foo: 0.11134742452557367 }
withConstant() // => { foo: 0.11134742452557367 }

const withMethod = Fabricator({ foo: () => Math.random() })
withMethod('withMethod') // => { foo: 0.4426388385403983 }
withMethod('withMethod') // => { foo: 0.572825488636862 }
withMethod('withMethod') // => { foo: 0.4322506522885017 }

Fabricator.times()

If you need to quickly generate more than one object you can use Fabricator.times():

const people = userFabricator.times(2)
// => [{ id: 3, ... }, { id: 4, ... }]

const colleagues = userFabricator.times(2, { companyId: 5 })
// => [{ id: 5, companyId: 5 }, { id: 6, companyId: 6 }]

If you need a random number of items you can pass an object with the properties min and max:

userFabricator.times({ max: 5 }) // => a random length from 1 to 5
userFabricator.times({ min: 0, max: 5 }) // => a random length from 0 to 5
userFabricator.times({ min: 0 }) // => a random length from 0 to 10

sequence()

Sometimes it can be useful to have an increasing value for a field, for example id. You can do this with sequence()

sequence() // => 1
sequence() // => 2
sequence() // => 3

In some cases you might want to have different sequences, you can simply pass a sequence name:

sequence('user') // => 1
sequence('company') // => 1
sequence('user') // => 2
sequence('user') // => 3
sequence('company') // => 2

sequence.reset()

If you are checking the sequence id, for example if you do snapshot testing you want your sequence numbers to be the same every time you execute your test. In this case you can simply reset the sequence before running the test:

sequence('user') // => 1
sequence('company') // => 1
sequence('user') // => 2
sequence('company') // => 2

sequence.reset()

sequence('user') // => 1
sequence('company') // => 1
sequence('user') // => 2
sequence('company') // => 2

sequence.reset('company')

sequence('user') // => 3
sequence('company') // => 1
sequence('user') // => 4
sequence('company') // => 2