如果在 JavaScript 中的对象数组中找到对象，则返回对象的属性答案

【问题标题】：Return object's property if it is found into an array of objects in JavaScript如果在 JavaScript 中的对象数组中找到对象，则返回对象的属性
【发布时间】：2017-08-08 21:03:54
【问题描述】：

我有以下对象数组：

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"]
    }
];

我想定义一个函数lookUpProfile(firstName, prop)，用于输入数据：

lookUpProfile("Akira", "likes");

将返回：

["Pizza", "Coding", "Brownie Points"]

这是我到目前为止的解决方案，直到现在还没有返回：

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

有没有人想办法解决这个问题？谢谢

【问题讨论】：

标签： javascript arrays javascript-objects

【解决方案1】：

您可以尝试这样做。使用 .find() 函数 (ES6) 查找项目并使用括号 [] 语法返回适当的属性。

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 lookUpProfileES6(name, prop){
  var found = contacts.find(item => item.firstName === name);
  if(found){
      return found[prop];
  }
}

function lookUpProfileES5(name, prop){
  var found = null;
  for(var i = 0; i < contacts.length; i++){
      if(contacts[i].firstName === name){
         found = contacts[i];
         break;
      }
  }
  
  if(found){
      return found[prop];
  }
}

var resultES6 = lookUpProfileES6("Akira", "likes");
var resultES5 = lookUpProfileES5("Akira", "likes");

console.log(resultES6);
console.log(resultES5);

【讨论】：

【解决方案2】：

您的问题是您尝试使用带有数字索引的 for 循环遍历对象。你根本不需要第二个循环。可以很简单

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];
      }
    }
  }
}

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];
    }
  }
}

console.log(lookUpProfile("Akira", "likes"))

【讨论】：

【解决方案3】：

你的代码的问题是这一行：

for(var j = 0; j < contacts[i].length; j++){

这里没有必要再次尝试迭代。此外，contacts[i] 是一个对象，因此没有长度属性，因此您在比较 0 < undefined 始终为假。

这会导致您对属性的条件检查永远不会发生。除此之外， prop 是这里的访问器。因此，虽然它可能包含属性名称，但它不包含属性值。为了正确返回属性值，需要在当前对象上以[prop]的形式作为访问器使用。

去掉第二次迭代，正确访问联系人对象，你的函数就可以正常工作了。

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];
  }
 }
}

【讨论】：

【解决方案4】：

你可以这样做

// Create a function which will filter out the requirement
var filtered = function(name, likes) {
  var _toRet = ''
  contacts.filter(function(elem, index) {
    // check if the first name is same as requires
    // check if the object have property likes
    // Since the requirement is to search the likes array
    if (elem.firstName === name && elem.hasOwnProperty(likes)) {
      _toRet = elem[likes]  
    }
    return _toRet  // return from filter callback

  })
return _toRet  // return from the function
}

console.log(filtered('Akira', 'likes'))

DEMO

【讨论】：