javascript - 嵌套 if 语句 - 如何重构条件以在迭代时使用一个 if 语句

Question

我有一个对象数组:

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"]
  }
];

我已经编写了一个函数来迭代它们。

function lookUpProfile(name, prop) {  

  for ( i = 0; i < contacts.length; i++) {  
    if (contacts[i].firstName === name) {  
      if (contacts[i].hasOwnProperty(prop)) {                     
        return contacts[i][prop]     
      } else {
        return "No such property"; 
      }
    }
  }

return "No such contact"; 

}

console.log(lookUpProfile("Harry", "likes"));

我试图重构函数，因此我可以使用一个 if 语句和 AND 运算符，而不是使用两个嵌套的 if 语句。为什么我这样做是为了提高可读性，因为我发现嵌套的 ifs 很难阅读。当我这样做时，我没有得到预期的返回值——当对象确实存在时，我得到“没有这样的属性”。那么换句话说，为什么第二个功能不能正常工作？我是否打破了函数迭代的方式？

function lookUpProfile(name, prop) {  

  for (var i = 0; i < contacts.length; i++) {  
    if (contacts[i].firstName === name && contacts[i].hasOwnProperty(prop)) {                 
      return contacts[i][prop]     
    } else {
      return "No such property"; 
    }
  }
  return "No such contact"; 
}

console.log(lookUpProfile("Harry", "likes")); 

Answer 1

这里的问题是您要尝试做两件事。

1. 根据名字从数组中找到正确的对象。
2. 确定该对象是否具有特定属性，如果有则返回其值。

为此，有一个嵌套的 if 是有意义的。 2 位逻辑，2 个 if 语句。

你当然可以将它重构为不使用嵌套 ifs，首先尝试找到对象，然后检查该对象是否具有所需的属性:

function lookUpProfile(name, prop) {  
  var obj = contacts.find(c => c.firstName === name);
  if(!obj)
     return "No such contact";
     
  if(obj.hasOwnProperty(prop))
     return obj[prop];
     
  return "No such property";
}


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"]
  }
];


console.log(lookUpProfile("Harry", "likes")); 
console.log(lookUpProfile("Harry", "foo")); 
console.log(lookUpProfile("Bob", "likes"));