创建一个撰写函数javascript [英] Create a compose function javascript

问题描述

我需要一个组成其他函数的函数以及一个值参数。例如：

I would need a function that composes other function as well as taking a value parameter. For example:

var doubleTheValue = function(val) { return val * 2; }
var addOneToTheValue = function(val) { return val + 1; }
compose(5, doubleTheValue, addOneToTheValue)-> 11

最重要的是它必须接受任意数量的功能



我尝试了什么：



我知道可以在某处找到解决方案网络，但我来得非常接近我只是不明白我做的错误

The most important thing is that it has to accept any number of functions

What I have tried:

I know that might be possible to find a solution somewhere on the web but I came very close I just don`t understand the mistake I had made

function compose(val, fn, fn1) {
var args = [].slice.call(arguments);
  
  for(var i = args.length - 1; i > 0; i--){
    var a = args[i].call(this, args[0])
  }
 return a
}
compose(5, doubleTheValue, addOneToTheValue) -> 10

出于某种原因，它会忽略第一种方法产生10，为什么？

For some reason it produces 10 ignoring the first method, why?

推荐答案

这里有两个明显的问题：



1）你总是传递 val 到组合函数，忽略从前一个组合函数返回的值。



2）你以相反的顺序调用组合函数：（5 + 1）* 2 而不是（5 * 2）+ 1 。



所以你的代码相当于：

Two obvious problems here:

1) You're always passing val to the composed functions, ignoring the value returned from the previous composed function.

2) You're calling the composed functions in reverse order: (5 + 1) * 2 instead of (5 * 2) + 1.

So your code is equivalent to:

val = 5;
a = addOneToTheValue(val); // = 6
a = doubleTheValue(val);   // = 10
return a;

而不是：

instead of:

val = 5;
a = val; // = 5
a = doubleTheValue(a);   // = 10
a = addOneToTheValue(a); // = 11
return a;

尝试这样的事情：

Try something like this:

function compose(val){
    var result = val;
    
    for (var i = 1; i < arguments.length; i++){
        result = arguments[i].call(this, result);
    }
    
    return result;
}

compose(5, doubleTheValue, addOneToTheValue); -> 11

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