var greeting = (firstName, lastName) => 'hello, ' + firstName + ' ' + lastName
var toUpper = str => str.toUpperCase()
var fn = compose(toUpper, greeting)
console.log(fn('jack', 'smith'))

compose接受函數(shù)作為參數(shù)，從右向左執(zhí)行，返回類型函數(shù)
fn()全部參數(shù)傳給最右邊的函數(shù)，得到結(jié)果后傳給倒數(shù)第二個(gè)，依次傳遞

compose的實(shí)現(xiàn)

var compose = function(...args) {
    var len = args.length // args函數(shù)的個(gè)數(shù)
    var count = len - 1
    var result
    return function func(...args1) { // func函數(shù)的args1參數(shù)枚舉
        result = args[count].call(this, args1)
        if(count > 0) {
            count --
             return func.call(null, result) // result 上一個(gè)函數(shù)的返回結(jié)果
        } else {
              //回復(fù)count初始狀態(tài)
              count = len -1
              return result
        }
    }
     
}