使用 indexOf 搜索 JSON object 返回 undefined

Question

I have JSON objects of chat messages in messages.json, as seen below:

[
  {
   "sender": "Bob",
   "text": "Hi, how are you?"
  },
  {
   "sender": "James",
   "text": "Good, you?"
  }
]

I want to search messages for the index of a term received from a text input. However when I run the following code, I receive "undefined" in the console.

const handleChange = (event) => {
  const result = messages.filter((message) => {
    return message.text.indexOf(event.target.value);
  });
  console.log(result);
};

Why is it returning undefined?

Answer 1

indexOf returns 0 if it found at the first character, which evaluates to FALSE. Try it with

return message.text.indexOf(event.target.value) > -1

Answer 2

indexOf() returns 0 based index so you need to convert it to boolean to avoid false positives. Also event.target.value might be empty, or has a different case.

I recommend making sure both values are defined and converting both strings to same case toLowerCase() before comparison

 const messages = [{ "sender": "Bob", "text": "Hi, how are you?" }, { "sender": "James", "text": "Good, you?" } ] const result = messages.filter((message) => { return message.text.toLowerCase().indexOf("good") >= 0; }); console.log(result);

Answer 3

Since message is array, indexOf won't work, you need to iterate to find single msg, use find() for that, to find multiple instances use filter()

   const handleChange = (event) => {
          const result = message.find(i=>i.text.toLowerCase().indexOf(event.target.value.toLowerCase()));
          console.log(result);
        };