javascript - 在 if 条件语句中访问 Javascript 对象，可以做到吗？

Question

这是我在免费代码训练营挑战“Profile Lookup”中的代码，我被这段代码卡住了，我的问题是 if 条件，如何让测试用例进入我的第一个 if 条件？

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

lookUpProfile("Harry", "likes");

我应该得到的是“likes”的值，也就是["Hogwarts", "Magic", "Hagrid"]，要做到这一点，它应该进入第一个if条件，并且有问题。

Answer 1

你的问题是你提前回来了。无论如何，如果满足任何条件，您总是会返回 contacts 集合的第一次迭代。您需要做的是将答案存储在循环外的局部变量中，然后返回该值。这样做可以确保您已经完成所有迭代而不会过早返回。

试试这个:

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 result = undefined;
  for (var i = 0; i < contacts.length; i++) {
    if (contacts[i].firstName === firstName) {
      result = contacts[i];
    } 
  }

  if (result === undefined) {
    return "No such contact";
  }
  if (result.hasOwnProperty(prop) === false) {
    return "No such property";
  }

  return result[prop];
}

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

一种更实用和惯用的方法是使用数组方法，例如 filter 。