javascript - 自由代码营 : Record Collection return "Cannot read property ' push' of undefined"

Question

挑战是来自 Freecodecamp 的“Basic JavaScript: Record Collection”。挑战是更新 JSON 格式的记录集合。

这是我编写的代码:

var collection = {
  "2548": {
    "album": "Slippery When Wet",
    "artist": "Bon Jovi",
    "tracks": [
      "Let It Rock",
      "You Give Love a Bad Name"
    ]
  },
  "2468": {
    "album": "1999",
    "artist": "Prince",
    "tracks": [
      "1999",
      "Little Red Corvette"
    ]
  },
  "1245": {
    "artist": "Robert Palmer",
    "tracks": []
  },
  "5439": {
    "album": "ABBA Gold"
  }
};
// Keep a copy of the collection for tests
var collectionCopy = JSON.parse(JSON.stringify(collection));


// Only change code below this line
function updateRecords(id, prop, value) {
  if (prop !== "tracks" && value !== "") {
    collection[id][prop] = value;
  } else if (prop === "tracks" && value !== "") {
    collection[id][prop].push(value);
  } else if (value == "") {
    delete collection[id][prop];
  } else if (prop === "tracks") {
    collection[id][prop] = [value];
  }


  return collection;
}

// Alter values below to test your code
updateRecords(5439, "artist", "ABBA");

它满足除一项要求之外的所有要求:

After updateRecords(5439, "tracks", "Take a Chance on Me"), tracks should have "Take a Chance on Me" as the last element.

当我检查控制台时，我得到了这个声明

Cannot read property 'push' of undefined

看起来代码认为push(应该是一个函数)实际上是一个对象属性。

如何修复它？

如果您想详细了解此挑战，请点击以下链接: https://guide.freecodecamp.org/certifications/javascript-algorithms-and-data-structures/basic-javascript/record-collection/

Answer 1

目前，您的代码永远不会达到 else if (prop === "tracks") 条件。如果 prop === "tracks" ，它将转到 prop === "tracks"&& value !== "" 条件并尝试推送 value 到 tracks 数组。如果id的tracks数组不存在(例如5439)，它将抛出错误。因此，您可以按如下方式更改条件

检查属性是否为tracks。在此 if 条件内检查 collection[id][prop] 是否具有值。如果是，则将其推送到数组中。否则，添加一个新数组，如下所示 [value]

function updateRecords(id, prop, value) {
  if (prop === "tracks" && value !== "") {

    // check if tracks exists
    if (collection[id][prop])
      collection[id][prop].push(value)
    else
      collection[id][prop] = [value]; // create a new array

  } else if (value != "") {
    collection[id][prop] = value;
  } else if (value == "") {
    delete collection[id][prop];
  }

  return collection;
}

这是一个工作片段:

var collection={2548:{album:"Slippery When Wet",artist:"Bon Jovi",tracks:["Let It Rock","You Give Love a Bad Name"]},2468:{album:"1999",artist:"Prince",tracks:["1999","Little Red Corvette"]},1245:{artist:"Robert Palmer",tracks:[]},5439:{album:"ABBA Gold"}};

// Keep a copy of the collection for tests
var collectionCopy = JSON.parse(JSON.stringify(collection));

// Only change code below this line
function updateRecords(id, prop, value) {
  if (prop === "tracks" && value !== "") {
  
    if(collection[id][prop])
      collection[id][prop].push(value)
    else
      collection[id][prop] = [value]
  
  } else if (value != "") {
    collection[id][prop] = value;
  } else if (value == "") {
    delete collection[id][prop];
  }

  return collection;
}

// Alter values below to test your code
updateRecords(5439, "artist", "ABBA");
updateRecords(5439, "tracks", "Take a Chance on Me");

console.log(collection[5439])