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问If和Return语句问题
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Stack Overflow用户

提问于 2018-04-30 07:16:49

回答 4查看 78关注 0票数 1

我的错误在哪里？我知道这与if语句与循环相关的位置有关，但我不能确定。目标是让函数检查对象是否具有某个属性，然后返回该属性。

//Setup
var contacts = [
    {
        "firstName": "Akira",
        "lastName": "Laine",
        "number": "0543236543",
        "likes": ["Pizza", "Coding", "Brownie Points"]
    },
    {
        "firstName": "Harry",
        "lastName": "Potter",
        "number": "0994372684",
        "likes": ["Hogwarts", "Magic", "Hagrid"]
    },
    {
        "firstName": "Sherlock",
        "lastName": "Holmes",
        "number": "0487345643",
        "likes": ["Intriguing Cases", "Violin"]
    },
    {
        "firstName": "Kristian",
        "lastName": "Vos",
        "number": "unknown",
        "likes": ["Javascript", "Gaming", "Foxes"]
    }
];


function lookUpProfile(firstName, prop) {
// Only change code below this line
 for (var i = 0; i < contacts.length; i++) {

    if (contacts[i].firstName === firstName) {
     if (contacts[i].hasOwnProperty(prop)) {
       return contacts[i][prop];
     }   
   } 

   else if (firstName !== contacts[i].firstName) {
     return "No such contact";
   }

   return "No such property";
 } 




// Only change code above this line
}

// Change these values to test your function
lookUpProfile("Kristian", "lastName");

javascript

回答 4

Stack Overflow用户

发布于 2018-04-30 07:26:08

正如我在注释中所说的，您需要移动失败条件，以便for循环能够在返回之前检查必要的索引：

var contacts = [{
    "firstName": "Akira",
    "lastName": "Laine",
    "number": "0543236543",
    "likes": ["Pizza", "Coding", "Brownie Points"]
  },
  {
    "firstName": "Harry",
    "lastName": "Potter",
    "number": "0994372684",
    "likes": ["Hogwarts", "Magic", "Hagrid"]
  },
  {
    "firstName": "Sherlock",
    "lastName": "Holmes",
    "number": "0487345643",
    "likes": ["Intriguing Cases", "Violin"]
  },
  {
    "firstName": "Kristian",
    "lastName": "Vos",
    "number": "unknown",
    "likes": ["Javascript", "Gaming", "Foxes"]
  }
];

function lookUpProfile(firstName, prop) {
  for (var i = 0; i < contacts.length; i++) {
    if (contacts[i].firstName === firstName) {
      if (contacts[i].hasOwnProperty(prop)) {
        return contacts[i][prop];
      }

      return "No such property";
    }
  }

  return "No such contact";
}

console.log(lookUpProfile("Kristian", "lastName"));

或者，您可以通过使用Array#find()来采用稍微更函数化的编程方法

var contacts = [{
    "firstName": "Akira",
    "lastName": "Laine",
    "number": "0543236543",
    "likes": ["Pizza", "Coding", "Brownie Points"]
  },
  {
    "firstName": "Harry",
    "lastName": "Potter",
    "number": "0994372684",
    "likes": ["Hogwarts", "Magic", "Hagrid"]
  },
  {
    "firstName": "Sherlock",
    "lastName": "Holmes",
    "number": "0487345643",
    "likes": ["Intriguing Cases", "Violin"]
  },
  {
    "firstName": "Kristian",
    "lastName": "Vos",
    "number": "unknown",
    "likes": ["Javascript", "Gaming", "Foxes"]
  }
];

function lookUpProfile(firstName, prop) {
  const contact = contacts.find(
    contact => contact.firstName === firstName
  );
  
  if (contact === undefined) {
    return "No such contact";
  }
  
  if (contact.hasOwnProperty(prop)) {
    return contact[prop];
  }
  
  return "No such property";
}

console.log(lookUpProfile("Kristian", "lastName"));

票数 2

Stack Overflow用户

发布于 2018-04-30 07:23:38

您的语句return "No such property";应该在for循环之外。在for循环中，该语句在第一次迭代后终止循环。

此外，您不需要else if (...，因为您将从for循环外部返回它。

//Setup
var contacts = [
    {
        "firstName": "Akira",
        "lastName": "Laine",
        "number": "0543236543",
        "likes": ["Pizza", "Coding", "Brownie Points"]
    },
    {
        "firstName": "Harry",
        "lastName": "Potter",
        "number": "0994372684",
        "likes": ["Hogwarts", "Magic", "Hagrid"]
    },
    {
        "firstName": "Sherlock",
        "lastName": "Holmes",
        "number": "0487345643",
        "likes": ["Intriguing Cases", "Violin"]
    },
    {
        "firstName": "Kristian",
        "lastName": "Vos",
        "number": "unknown",
        "likes": ["Javascript", "Gaming", "Foxes"]
    }
];


function lookUpProfile(firstName, prop) {

 for (var i = 0; i < contacts.length; i++) {
  if (contacts[i].firstName === firstName) {
   if (contacts[i].hasOwnProperty(prop)) {
     return contacts[i][prop];
   }   
  } 
 } 

 return "No such property";
}

// Change these values to test your function
console.log(lookUpProfile("Kristian", "lastName"))
console.log(lookUpProfile("Sherlock", "lastName"))

OR:如果您对Array#filter很熟悉：

//Setup
var contacts = [
    {
        "firstName": "Akira",
        "lastName": "Laine",
        "number": "0543236543",
        "likes": ["Pizza", "Coding", "Brownie Points"]
    },
    {
        "firstName": "Harry",
        "lastName": "Potter",
        "number": "0994372684",
        "likes": ["Hogwarts", "Magic", "Hagrid"]
    },
    {
        "firstName": "Sherlock",
        "lastName": "Holmes",
        "number": "0487345643",
        "likes": ["Intriguing Cases", "Violin"]
    },
    {
        "firstName": "Kristian",
        "lastName": "Vos",
        "number": "unknown",
        "likes": ["Javascript", "Gaming", "Foxes"]
    }
];


function lookUpProfile(firstName, prop) {
  var res = contacts.filter(p => p.firstName === firstName);
  if (res.length > 0 && res[0].hasOwnProperty(prop)) {
   return res[0][prop];
  } 

 return "No such property";
}

// Change these values to test your function
console.log(lookUpProfile("Kristian", "lastName"))
console.log(lookUpProfile("Sherlock", "lastName"))

票数 1

Stack Overflow用户

发布于 2018-04-30 07:33:49

在Mamun之前，我已经写出了大部分内容，但我想更多地谈谈这个答案和您正在做的事情

对于我的解决方案，我只是简单地将数组过滤为只具有正确名字的内容。如果您确定您的元素将具有不同的名字，那么这是一个很好的解决方案，因为您应该只期望过滤后的数组的长度为0或1。现在，缺点是Array.filter()在整个数组长度中运行，甚至在我们找到person之后也会继续运行。对于一个很短的数组，就像这个例子一样，这不是问题。对于一个有10,000个元素的数组，我们的person是第一个搜索的，有点性能问题。

另一个问题是:如果你有多个名字相同的人，会发生什么？过滤后的数组将大于1，但我们只会使用第一个结果--可能会有问题。

此外，如果您计划频繁地查找信息，则可能需要考虑使用所谓的“散列映射”--它们是听起来很复杂的名称，非常简单。

是什么让一个条目与众不同？在大多数情况下，我们有来自数据库的数据附带的一些不同的ID，但在这种情况下，我们没有。然后我们必须问自己，是什么让"Kristian Vos“不同于"Krtistian Paule”(假设两者都在相同的拉取数据中)。使用我们所知道的关于对象的重要信息(在本例中是名字+姓氏)，我们创建一个唯一的键来将数据存储在对象中。这样，我们可以通过简单地使用映射键访问对象来更快地查找事物。

我的观点是:仔细考虑如何处理您的解决方案，并了解小型数据集通常很容易连续遍历，但是假设由于某种原因，您的数组包含10,000或100,000个条目--您是否以最合理的方式处理数据？

var contacts = [
    {
        "firstName": "Akira",
        "lastName": "Laine",
        "number": "0543236543",
        "likes": ["Pizza", "Coding", "Brownie Points"]
    },
    {
        "firstName": "Harry",
        "lastName": "Potter",
        "number": "0994372684",
        "likes": ["Hogwarts", "Magic", "Hagrid"]
    },
    {
        "firstName": "Sherlock",
        "lastName": "Holmes",
        "number": "0487345643",
        "likes": ["Intriguing Cases", "Violin"]
    },
    {
        "firstName": "Kristian",
        "lastName": "Vos",
        "number": "unknown",
        "likes": ["Javascript", "Gaming", "Foxes"]
    }
];

function lookUpProfile(firstName, prop){
  let profile = contacts.filter(person=> person.firstName == firstName);
  //Get only the person who has the same first name
  if(!profile.length) return false;
  //If the length is 0, then !0 will be truthy and the function will immediately return false
  profile = profile[0];
  //this is pure laziness, you could just alter the next line to read profile[0][prop] but I'll be honest i did this for visual appeal
  return profile[prop] || false;
  // this notation is fucky -- if the property is set on the profile, then it will return that value.
  // if it is not set, it'll return undefined, which is a falsey value and will therefore move over to the other side of the || and return that value, which is false.
}

console.log(lookUpProfile('Kristian', 'lastName'));

票数 0

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原文链接：

https://stackoverflow.com/questions/50092184

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