LOGIC BLOCK

v1.5.0

Logic block is a JavaScript/Typescript library for bundling bussiness logic of your data to common containers called blocks.

Features:

• Declarative - defining your logic (or block) as simple as defining object in JS
• Modular - every defined block is a simple bunch of logic, that is self-sufficient, and after it was defined you can use it in any kind of JS code
• Automatic - when create instance of block, it grabs all logic and runs logic automatically, and provide simple result as object
• Flexible - you allow to build complex block from little block or you can extend block with new rules
• Independent - every block is independent on the environment where it uses, the namespace of block is local, but it allow complex blocks to get values inside nested

And of course, it is very simple in usage.

Installation

Just add it to project dependencies

yarn add logic-block
// or
npm install --save logic-block

Usage

IMPORTANT: The logic-block lib is not an app state handler lib (like redux). Every block is just a runner of data logic.

1. Define a block with couple of rules (field reducers)

import Block, { value, fields } from 'logic-block'

const emailBlock = Block({
  email:
    value(),
  isCompanyEmail:
    fields(email => email.endsWith('@comp.com')) }, ['email'])
})

2. Create an instance of it

const initialValues = { email: 'default@comp.com' }
const instance = emailBlock(initialValues)

3. Run instance to get the output results

const initialState = instance()
// now initialState is
// { email: 'default@comp.com', isCompanyEmail: true }

4. Update value when you need

// here you put only data which were changed
const newState = instance({ email: 'non-company@mail.com' })

// now newState is
// { email: 'non-company@mail.com', isCompanyEmail: false }

That's it. For more real-world example check the code in example folder.

API

Block

Block is just a builder function that provides factory of instances of defined block-scheme.

Result

BlockFactory

BlockFactory

BlockFactory is a function which process data from input to the output calculated with scheme.

You get BlockFactory from block factory (you get block factory as result of call Block function).

Result

BlockInstance

BlockInstance

BlockInstance is a function that takes changes in data and provide as a result calculated value based on a scheme

You get BlockInstance on every call of BlockFactory.

wrapHandler

wrapHandler allows you to define your handler for block

Example:

import Block, { wrapHandler, value } from 'logic-block'
// define block for checking emails
const EmailBlock = Block({
  email: value(),
  done: value(false),
  isValid: value(false)
}, wrapHandler(() => {
  // that namespace you can use as constructor, here you can cache values between updates of block
  // or initialize some resources for running handler
  let initialRender = true

  return async (value, update, oldValue) => {
    // this protector make us sure that it will be run only on first render of block
    if (!initialRender) return
    initialRender = false

    const { email } = value
    if (email?.endsWith('@company.com')) {
      update({ done: false, isValid: false })

      const isValid = await api.checkEmailInternal(email)
      update({ done: true, isValid })
    }
  }
}))

// create instance with setted checking email as initial values
// add handler of updates, because our checking is async
const emailChecker = EmailBlock({
  email: 'test@company.com'
}, {
  handleUpdate: ({ isValid, done }) => { if (done) console.log('is valid email', isValid) }
})
// run the block
emailChecker()

createHandler

createHandler is a shortcut function for wrapHandler, that gets as a parameter handler of updates. Example:

import Block, { wrapHandler, value } from 'logic-block'

const progress = Block({
  percent: value(0),
  done: value(false)
}, createHandler((value, update, oldValue) => {
  if (propChanged(value, oldValue, 'a') && value.a === 100) {
    update({ done: true })
  }
}))

createFieldReducer

createFieldReducer creates the field reducer that applies some metadata from scheme and returns new value based on it

Example:

import getPath from 'lodash/get'
import Block, { createFieldReducer } from 'logic-block'

// the reducer that applies dependencies, which we can use in actual reducer function
const isUpgraded = (depField: string) => {
  return createFieldReducer((value, oldValue, path) => {
    if (getPath(value, depField) > getPath(oldValue, depField)) {
      return 'upgraded'
    }
    return 'downgraded'
  })
}

const block = Block({
  a: createFieldReducer((value, _, path) => {
    return getPath(value, path, getPath(oldValue, path))
  }),
  b: isUpgraded('a')
})

updateArray

updateArray creates the update value for passing to the render method for block instance, use it if you have any kind of array in your schema. You can use it anywhere for updating block instance value (initialization, rendering call, handler)

Example:

import Block, { updateArray } from 'logic-block'
import SectionBlock from './SectionBlock'

const block = Block({
  sections: [
    SectionBlock('examples'),
    SectionBlock('links'),
    SectionBlock('reminders')
  ]
})
// use for update 3-rd section with new value in initial values
const instance = block({ sections: updateArray(2, { title: 'reminder tip' }) })
// or update 2-nd section with new value in the rendering call
const result = instance({ sections: updateArray(1, { title: 'scrap booking link' } ) })

List of default reducers

1. value(defaultValue: any | (currentValue) => any) - reducer that returns new provided value as is, and set the default value on initial render if initial value was not provided
2. fields(reducerFn: Function, dependencies: Array) - reducer that gets as argument reducer fn, and list of fields which it passes to reducerFn. Example:

Block({
  a: value(1),
  b: fields((a, currentValue, currentBlockValue) => a + 1, ['a'])
})

3. memo(reducerFn: Function, dependencies: Array) - the same behaviour as in fields, except that reducerFn, will run only if dependecies values were changed. And also it can put the value if you update field directly. Example:

const block = Block({
  html: value(''),
  version: value(1),
  formattedMessage: memo((html, currentValue, currentBlockValue) => reallyHardLogicForHandlingHTML(html), ['html'])
})

// here the formatted message will handled by reducer
block({ html: DEFAULT_HTML })
// here the formatted message will set to SOME_CUSTOM_FORMATTED_MESSAGE value
block({ formattedMessage: SOME_CUSTOM_FORMATTED_MESSAGE })
// here the formatted message won't be changed
block({ version: 22 })

4. reduce(reducerFn: (value: Object, fieldValue: any) => any) - reducer simply gets new value of block and new value of field
5. option(defaultValue: any, options: Array) - reducer that allows as result only values at options list Example:

const block = Block({
  // initial value if not provided will be 'list'
  type: option('list', ['list', 'grid'])
})

// here the type will change on 'grid'
block({ type: 'grid' })
// here the type will stay as 'grid'
block({ type: 'unreginstered_type' })

List of default handlers

1. memoHandler(handlerFn: Function, dependencies: Array) - this handler like as memo field reducer, runs only if dependecy values were changed.

Example

const block = Block({
  // initial value if not provided will be 'list'
  type: option('list', ['list', 'grid']),
  classnames: value([])
}, memoHandler(async (type, update, value, oldValue) => {
  // handler will run only if type is changed
  const classnames = await api.getClassNames(type)
  update({ classnames: merge(value.classnames, classnames) })
}, ['type']))

Using memoHandler with typescript

You need to provide all the generic types explicitly.

type BlockValues = { ... };
Block({ ... }, memoHandler(() => {}, ['someNumberDep', ...]))

2. onCreateHandler(handlerFn: (value, update, oldValue) => void) - this handler run the handlerFn only when new instance was created

Example:

const block = Block({
  // initial value if not provided will be 'list'
  type: option('list', ['list', 'grid']),
  possibleConfigs: value()
}, onCreateHandler(async (value, update) => {
  // handler will run only when new instance created
  const configs = await api.getPossibleConfigs(type)
  update({ possibleConfigs: configs })
}, ['type']))

3. composeHandlers(...handlers: Array) - use this handler for attaching multiple handlers on one block.

Important: it works in the next way: when block instance renders it invokes all handlers in composed func one by one, if one handler in the chain updates value it invokes next handler with updated value. If any of handler updated value it will invoke this all handlers one more time after all handlers run.

Example:

const block = Block({
  // ...
}, composeHandlers(
  onCreateHandler(fn0),
  memoHandler(fn1, ['a']),
  memoHandler(fn2, ['b'])
))

List of block changers

Block changer is a tools which provide some operations on block factory instances. For example you can extend one block with other, you can change handler, etc.

1. extend(...blockArgs: Array) => BlockFactory - this changer function takes list of block factories or objects (which will be used as schemes) and create new block factory by merging schemes from right to left. That means that more righter blocks or schemes in arguments will override scheme fields in all lefter block factory. IMPORTANT: it does not apply handlers from blocks to the result block

const newBlock = extend(Block(s1), Block(s2), Block(s3), scheme4)

2. copy(block: BlockFactory) => BlockFactory - this changer function create full copy of passing block factory, also it is copying block handler

// newBlock will be full copy of b1
const b1 = Block(scheme)
const newBlock = copy(b1)

3. inherit(parentBlock: BlockFactory | Object, extendingBlock: BlockFactory | Object, extraHandler?: BlockHandler) => BlockFactory - this changer function extends schemes from parentBlock to extendingBlock and combines parent's block handler with extra handler if they exists

const CarBlock = inherit(WheelsBlock, CabinBlock, carExtraHandler)

4. withHandler(block: BlockFactory | Object, handler: BlockHandler) => BlockFactory - this changer function applies block or object and returns new block with replaced handler. IMPORTANT: it does not combine handlers from original block and handler which passed as argument, it sets as handler only passed block handler.

const block = Block({}, handler1)
// blockWithOtherHandler will have only handler2 as handler
const blockWithOtherHandler = withHandler(block, handler2)

Motivation

I have created this lib for one of my projects, where the same business-logic should be using on different clients. They had different UI, API, servers, code, platforms, but all them uses the pretty same logic for data. And I thought about implementing business logic as separate library with minimal dependecies (the only dependency is logic-block). So the logic-block solved my problem excellently.

Logic blocks in combination with handlers gives simple and powerful solution for writing code that should be shared between projects.

Also it gives enough level of flexability and declarativeness.

So I wanted to share it with the community.

Author

Ilya Melishnikov

LICENSE

MIT