重新创建JavaScript的减少功能 [英] Recreating JavaScript's reduce function

问题描述

这帮助我理解了很多，但我有一个小问题：
如何重新创建Underscore.js _.reduce方法？
当我插入数组时，它正常工作，但对象不起作用。我弄不明白。对于我应该改变的内容，我将不胜感激。我评论了我认为应该改变的地方，但我很困惑我需要改变它。我也创建了我自己的每个功能。

你可以在这里找到我的代码： http：// goo。 gl / 6RU9Bc

任何建议都会非常有帮助。谢谢!!

这是我到目前为止：

  var myArray = [1,2,3,4,5]; 
 
 var myObject = {
 num1：1，
 num2：2，
 num3：3 
}; 
 
函数each（collection，callback）{
 if（Array.isArray（collection））{
 for（var i = 0，l = collection.length; i  callback（collection [i]）; 
}; 
} else if（collection ===object）{
 for（var collection in collection）{
 callback（collection [prop]）; 
}; 
} 
} 
 
函数multiply（num，num2）{
 return num * num2; 
 
 
函数reduce（collection，callback，accumulator）{
 each（collection，function（element）{
 if（accumulator === undefined）{
 return accumulator = element; //这里是问题吗？为什么？我不明白。
} else {
 return accumulator = callback（accumulator，element）; 
}; 
}）; 
 
返回累加器; 
}; 
 
 console.log（reduce（myArray，multiply））; // 120 
 console.log（reduce（myArray，multiply，5））; // 160 
 console.log（reduce（myObject，multiply））; //返回undefined 
 console.log（reduce（myObject，multiply，5））; //返回5 
  

解决方案

正如@Yeldar Kurmangaliyev ，你需要改变它：

  if（collection ===object）
 
  if（typeof（集合）===object）
  
以下是固定代码：
  var myArray = [1,2,3,4,5]; 
 
 var myObject = {
 num1：1，
 num2：2，
 num3：3 
}; 
 
函数each（collection，callback）{
 if（Array.isArray（collection））{
 for（var i = 0，l = collection.length; i  callback（collection [i]）; 
}; 
} else if（typeof（collection）===object）{
 for（var collection in collection）{
 callback（collection [prop]）; 
}; 
} 
} 
 
函数multiply（num，num2）{
 return num * num2; 
 
 
函数reduce（collection，callback，accumulator）{
 each（collection，function（element）{
 if（accumulator === undefined）{
 return accumulator = element; //这里是问题吗？为什么？我不明白。
} else {
 return accumulator = callback（accumulator，element）; 
}; 
}）; 
 
返回累加器; 
}; 
 
 console.log（reduce（myArray，multiply））; // 120 
 console.log（reduce（myArray，multiply，5））; // 600 
 console.log（reduce（myObject，multiply））; // 6 
 console.log（reduce（myObject，multiply，5））; // 30 
  
 
I'm trying to recreate the reduce method but as the original function.

This helped me to understand a lot but I have one little issue:
How to re-create Underscore.js _.reduce method?
When I plug in arrays it works right, but objects don't work. I get undefined. I would appreciate advice on what I should change. I commented where I think I should change something but I'm confused exactly what I need to change it to. I also created my own each function. 

You can find my code here: http://goo.gl/6RU9Bc

Any advice would be super helpful. Thank you!!

This is what I have so far:
var myArray=[1,2,3,4,5];

var myObject={
  num1:1,
  num2:2,
  num3:3
};

function each(collection, callback){
  if(Array.isArray(collection)) {
    for(var i=0, l=collection.length; i<l; i++){
      callback(collection[i]); 
    };
  }else if(collection === "object") {
    for(var prop in collection){
       callback(collection[prop]);
    };
  }
}

function multiply(num, num2){
  return num*num2;
}

function reduce(collection, callback, accumulator){
  each(collection, function(element){
    if(accumulator === undefined) {
      return accumulator = element; // is the problem here? Why? I don't understand.
    }else {
      return accumulator = callback(accumulator, element);
    };   
});

return accumulator;
};

console.log(reduce(myArray, multiply)); // 120
console.log(reduce(myArray, multiply, 5)); // 160
console.log(reduce(myObject, multiply)); // returns undefined
console.log(reduce(myObject, multiply, 5)); // returns 5

解决方案
As pointed out by @Yeldar Kurmangaliyev, you need to change this:
if(collection === "object")
to:
if(typeof(collection) === "object")
Here is the fixed code:
var myArray=[1,2,3,4,5];

var myObject={
  num1:1,
  num2:2,
  num3:3
};

function each(collection, callback){
  if(Array.isArray(collection)) {
    for(var i=0, l=collection.length; i<l; i++){
      callback(collection[i]); 
    };
  }else if(typeof(collection) === "object") {
    for(var prop in collection){
       callback(collection[prop]);
    };
  }
}

function multiply(num, num2){
  return num*num2;
}

function reduce(collection, callback, accumulator){
  each(collection, function(element){
    if(accumulator === undefined) {
      return accumulator = element; // is the problem here? Why? I don't understand.
    }else {
      return accumulator = callback(accumulator, element);
    };   
});

return accumulator;
};

console.log(reduce(myArray, multiply)); // 120
console.log(reduce(myArray, multiply, 5)); // 600
console.log(reduce(myObject, multiply)); // 6
console.log(reduce(myObject, multiply, 5)); // 30


                        
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