Question

我试图重新创建reduce方法，但是作为原始函数。

这让我了解了很多，但我有一个小问题： How to re-create Underscore.js _.reduce method? 当我插入数组时，它可以正常工作，但对象不起作用。我得到了不确定。我很欣赏有关我应该改变的建议。我评论了我认为应该改变的地方，但我确切地想要改变它所需要的东西。我还创建了自己的每个功能。

您可以在此处找到我的代码：http://goo.gl/6RU9Bc

任何建议都会非常有帮助。谢谢!!

这是我到目前为止所做的：

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

Answer 1

正如@Yeldar Kurmangaliyev所指出的，你需要改变这个：

if(collection === "object")

为：

if(typeof(collection) === "object")

这是固定代码：

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

重新创建JavaScript减少功能

1 个答案: