JavaScript中的函数与命令模式，Java也有参考价值

const hour = 14
let greeting

if (hour < 18) {
  greeting = 'Good day';
} else {
  greeting = 'Good evening';
}

const isDay = hour => hour < 18
const getGreeting = hour => isDay(hour) ? 'Good Day' : 'Good Evening'
const greeting = getGreeting (hour)

let name = 'joel'

if (name != null) {
  name = name.toUpperCase()
}

函数范式：
isNotnull和toUpperCase市可重用的函数：

import when from 'mojiscript/logic/when'

const isNotNull = obj => obj != null
const toUpperCase = when (isNotNull) (string => string.toUpperCase ())

const name = 'joel'
const upperName = toUpperCase (name)


[b]数组相加[/b]

const values = [1, 2, 3]

let sum = 0
for (const x of values) {
  sum = sum + x
}

函数范式：
不将sum变成可变变量：

const values = [1, 2, 3]

const add = (x, y) => x + y
const sum = values.reduce(add)

[b]for/if[/b]
命令范式：

const values = [1, 2, 3, 4, 5]

let evens = []
for (const x of values) {
  if (x % 2 === 0) {
    evens.push(x)
  }
}

函数范式：
不要将evens成为可变：

import filter from 'mojiscript/list/filter'

const values = [1, 2, 3, 4, 5]

const isEven = num => num % 2 === 0
const evens = filter (isEven) (values)


[b]提前中断循环[/b]
命令范式：

const values = [1, 2, 3]
let sum = 0
for (const x of values) {
  if (x > 3) break
  sum = sum + x 
}

函数范式：
使用reduceWhile，类似reduce，能接受一个

import reduceWhile from 'mojiscript/list/reduceWhile'

const add = x => y => x + y
const lte3 = num => num <= 3

const sum = reduceWhile (() => lte3) (add) (0) (values)

命令范式：

const fn = temp => {
   if (temp === 0) return 'water freezes at 0°C'
   else if (temp === 100) return 'water boils at 100°C'
   else return `nothing special happens at ${temp}°C`
}

fn(0) //=> 'water freezes at 0°C'
fn(50) //=> 'nothing special happens at 50°C'
fn(100) //=> 'water boils at 100°C'

函数范式：

import cond from 'mojiscript/logic/cond'
import $ from 'mojiscript/string/template'

const fn = cond([
  [0, 'water freezes at 0°C'],
  [100, 'water boils at 100°C'],
  [() => true, $`nothing special happens at ${0}°C`]
])

fn(0) //=> 'water freezes at 0°C'
fn(50) //=> 'nothing special happens at 50°C'
fn(100) //=> 'water boils at 100°C'

[b]类
[/b]命令范式：

class Cat {
  constructor() {
    this.sound = 'Meow'
  }

  talk() {
    return this.sound
  }
}

const cat = new Cat()
const talk = cat.talk

cat.talk() //=> 'Meow'
talk() //=> Error: Cannot read property 'sound' of undefined

函数范式：

const cat = {
  sound: 'Meow'
}

const dog = {
  sound: 'Woof'
}

const talk = animal => animal.sound

talk (cat) //=> 'Meow'
talk (dog) //=> 'Woof'

检查空NULL

命令范式：

const toUpper = string => {
  if (string != null) {
    return string.toUpperCase()
  }
}

函数范式：

Maybe

Maybe

string