javascript - 我的元素有一个值，直到将方法 .toLowerCase 附加到它

Question

这是我的初始代码，可以完美运行。

const objNotes = [
  {},
  {
    title: "Be better",
    body: "Do better"
  },
  {
    title: "You are what you eat",
    body: "Eat well and responsibly"
  },
  {
    title: "Look good",
    body: "Work good"
  }
];

const findNote = (notes, noteTitle) => {
  const index = notes.findIndex((note, index) => {
    return note.title === noteTitle;
  });
  return notes[index];
};

const action = findNote(objNotes, "Look good");
console.log(action);

当我附加方法 .toLowerCase 时，如下所示，我得到:

TypeError: Cannot read property 'toLowerCase' of undefined

我不明白为什么。

const findNote = (notes, noteTitle) => {
  const index = notes.findIndex((note, index) => {
    return note.title.toLowerCase() === noteTitle.toLowerCase();
  });
  return notes[index];
};

Answer 1

您的第一个对象没有属性title，尝试toLowerCase()会引发错误。

在使用toLowerCase()之前可以检查对象中的属性是否存在:

const objNotes = [
  {},
  {
    title: "Be better",
    body: "Do better"
  },
  {
    title: "You are what you eat",
    body: "Eat well and responsibly"
  },
  {
    title: "Look good",
    body: "Work good"
  }
];

const findNote = (notes, noteTitle) => {
  const index = notes.findIndex((note, index) => {
    return note.title == undefined? '' : note.title.toLowerCase() === noteTitle.toLowerCase();
  });
  return notes[index];
};

const action = findNote(objNotes, "Look good");
console.log(action);