17. 组合函数原理模拟

const _ = require('lodash')

const reverse = arr => arr.reverse()
const first = arr => arr[0]
const toUpper = s => s.toUpperCase()

const f = _.flowRight( toUpper, first, reverse)
console.log(f(['one', 'two', 'three']))  // THREE

// 模拟 lodash 中的 flowRight
function compose (...arg) {
  return function(value) {
    return arg.reverse().reduce(function(acc, fn) {
      return fn(acc)
    }, value) 
  }
}

ES6写法

const compose = (...args) => value => args.reverse().reduce((acc, fn) => fn(acc), value)

const reverse = arr => arr.reverse()
const first = arr => arr[0]
const toUpper = s => s.toUpperCase()

const f = compose(toUpper, first, reverse)
console.log(f(['one', 'two', 'three']))  // THREE