Immutability

Functional programming

Pure functions

What is a perfect function

• Doesn't depend on higher scope
• Always returns the same results with the same arguments
• Can be used in memoization pattern
• Can be used in different environment
• Easy to test
• Can be run in parallel

function (a: number[]): number {
    return a.reduce((akk, num) => akk + num, 0);
}

Can it be run in parallel?

function (a: number[]): number {
    return a.reduce((akk, num) => akk + num, 0);
}

function todoApp(state = initialState, action) {
  switch (action.type) {
    case SET_VISIBILITY_FILTER:
      return Object.assign({}, state, {
        visibilityFilter: action.filter
      })
    default:
      return state
  }
}

Immutability

Immutable in JS

• Number
• String
• null
• undefined
• Boolean
• Symbol

const

freeze and seal

defineProperty

Object.defineProperty(obj, 'key', {
  enumerable: false,
  configurable: false,
  writable: false,
  value: 'static'
});

function todoApp(state = initialState, action) {
  switch (action.type) {
    case SET_VISIBILITY_FILTER:
      return Object.assign({}, state, {
        visibilityFilter: action.filter
      })
    default:
      return state
  }
}

How change it?

Copy everything!

Use immutable data structures

Array

LinkedList

Hashmap and set

Tire Tree

Operations

• Search
• Insert
• Delete

Tire hash map

How can we get it?

Map or Set?

Immutable.js