es6 还原 es5

Question

const compose = f => g => x => f(g(x));const f = compose (x => x * 4) (x => x + 3);f(2) // 20求一个化简后的compose!!!!!!.......还有为什么f(2)等于8

Answer 1

"use strict";

var compose = function compose(f) {

  return function (g) {

    return function (x) {

      return f(g(x));

    };

  };

};

var f = compose(function (x) {

  return x * 4;

})(function (x) {

  return x + 3;

});

f(2);

地址

可能给compose的参数换个名字更阅读一些?

var compose = function(a) {

    return function(b) {

        return function(c) {

            return a(b(c));

        };

    };

};

var f = compose(function(x) {

    return x * 4;

})(function(x) {

    return x + 3;

});

console.log(f(2));

调用的话一共有三次

var f = compose(function(x) {

    return x * 4;

})(function(x) {

    return x + 3;

});

两次

f(2)

一次

三次调用再拆为

var f1=compose(function(x) {

    return x * 4;

})

var f2 = f1(function(x) {

    return x + 3;

})

f2(2);

1. compose(function(x) {return x * 4;})即参数a为函数function(x) {return x * 4;}内部a(b(c))相当于对a调用内部参数x为b(c),得到function(b){return function(c){return b(c)*4}}

2. 此时 f1 = function(b){return function(c){return b(c)*4}}同样对f1的调用f1(function(x) {return x + 3;})相当与参数b为function(x){return x+3},内部b(c)相当于将c作为参数传入b中,得到function(c){return (c+3)*4}

3. 此时f2=function(c){return (c+3)*4},f2(2)=20

有点绕，可以拿笔和纸写一下。