javascript - For in 对象上的循环，以及 .find，返回 "undefined"

Question

我正在尝试循环访问一个对象 (objectToLoop) 并检查是否包含键 comments_text。如果是，我想检查 comments_text，如果 comments_text 中的 key 与 commentId 匹配，我想将 let item 设置为 comments_text 中的整个对象。

我尝试将 let item 设置为以下内容，但出现“未定义”:

{
 commenter_comment: "reedwe",
 commenter_handle: "FALCON1",
 commenter_uid: "ZALb0B3wZEWjfdFIUOxteJRl9Xu1",
 key: "-MlaKXBMXzXIBJMsZQNX"
}

感谢建议和反馈。

const commentId = "-MlaKXBMXzXIBJMsZQNX"

const objectToLoop = {
  comment: false,
  comments_text: {
    commenter_comment: "reedwe",
    commenter_handle: "FALCON1",
    commenter_uid: "ZALb0B3wZEWjfdFIUOxteJRl9Xu1",
    key: "-MlaKXBMXzXIBJMsZQNX"
  },
  handle: "TURTLE1",
  key: "-MkeOOUboKdOcC3Sannl",
  title: "hello2"
}

function returnMatchingComment(commentIdKey) {
  let item;
  for (const post in objectToLoop) {
    if (post.comments_text) {
      item = Object.values(post.comments_text).find(
        (comment) => comment.key === commentIdKey
      )
    };
    if (item) {
      break;
    }
  }
  return item
}
console.log(
  returnMatchingComment(commentId)
) 

Answer 1

您不需要使用for...in 循环。您可以首先使用 Object.prototype.hasOwnProperty() 检查 objectToLoop 是否具有属性 comments_text并检查是否 objectToLoop?.comments_text?.key == commentId。我使用了 ?. (可选链接)，这样如果 objectToLoop.comments_text 不存在，它只会返回 undefined 而不会抛出丑陋的错误错误。
示例:

const commentId = "-MlaKXBMXzXIBJMsZQNX"

const objectToLoop = {
  comment: false,
  comments_text: {
    commenter_comment: "reedwe",
    commenter_handle: "FALCON1",
    commenter_uid: "ZALb0B3wZEWjfdFIUOxteJRl9Xu1",
    key: "-MlaKXBMXzXIBJMsZQNX"
  },
  handle: "TURTLE1",
  key: "-MkeOOUboKdOcC3Sannl",
  title: "hello2"
}
if(objectToLoop.hasOwnProperty('comments_text') && objectToLoop?.comments_text?.key == commentId) { 
    let item = objectToLoop.comments_text;
    console.log(item)
}

老实说，我们甚至不需要 objectToLoop.hasOwnProperty('comments_text') ，就像可选链接一样(如前所述)，objectToLoop?.comments_text?.key == commentId<如果 objectToLoop.comments_text 不存在， 将返回 undefined；如果 objectToLoop.comments_text.key，则返回 false不等于commentId。
示例2:

const commentId = "-MlaKXBMXzXIBJMsZQNX"

const objectToLoop = {
  comment: false,
  comments_text: {
    commenter_comment: "reedwe",
    commenter_handle: "FALCON1",
    commenter_uid: "ZALb0B3wZEWjfdFIUOxteJRl9Xu1",
    key: "-MlaKXBMXzXIBJMsZQNX"
  },
  handle: "TURTLE1",
  key: "-MkeOOUboKdOcC3Sannl",
  title: "hello2"
}

if(objectToLoop?.comments_text?.key == commentId) { 
    let item = objectToLoop.comments_text;
    console.log(item)
}