How to specify an array index?

Question

How to get the index of an array? Now I get undefined as the result of executing the "blockCreate" function, I think this is because I do not specify the index of the array, although I should get true, how to automatically indicate the index for the array?

import React, { useState } from "react";
import "./styles.css";

export default function App() {
  const [array1, setArray1] = useState([{ number: 1 }]);
  const [array2, setArray2] = useState([{ number: 2 }]);

  const blockCreate = () => {
    return array1.find(items => {
      const bool = array2.find(i => i.number === items.number);
      console.log(bool);
    });
  };

  return (
    <div className="App">
      <div>{blockCreate()}</div>
    </div>
  );
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.6.3/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.6.3/umd/react-dom.production.min.js"></script>

Tell us more about what exactly you are trying to build. What blockCreate() is supposed to do, in particular? — Yevhen Horbunkov
– Yevhen Horbunkov, Commented Jan 31, 2020 at 23:40
find returns undefined when there is nothing found. The value of the first element in the array that satisfies the provided testing function. Otherwise, undefined is returned. — sissonb
– sissonb, Commented Jan 31, 2020 at 23:50
Array.find() doesn't return a boolean, instead it return the first element that matches the condition. developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/… — Dr4ke the b4dass
– Dr4ke the b4dass, Commented Jan 31, 2020 at 23:51

Dr4ke the b4dass · Accepted Answer · 2020-01-31 23:54:37Z

2

Array.find() doesn't return a boolean, instead it return the first element that matches the condition. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/find

It's quite obscure what you're trying to do, but I think what you looking for is Array.some() which return a boolean. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/some

answered Jan 31, 2020 at 23:54

Dr4ke the b4dass

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