Reactjs - get value from array

Question

I have a list of images, I want to get the name of the image that is in the zero position of the matrix.

As you can see in the image, the name is inside File. But when I try items[0].file or items[0]['file'] the error TypeError returns: Cannot read property 'file' of undefined

My code:

export function Multiple() {

    const handleChange = files => {
      files.map(file => {
        setItems(item => [
          ...item,
          {
            file,
            onRemove: handleOnRemove,
            onClick: handleOnClick
          }
        ]);
      });
    };
  
    const handleOnRemove = file => {
      setItems(item => [...item.filter(item => item.file.name !== file.name)]);
    };
  
    const handleOnClick = file => {
      getBase64(file)
      setNameImage(file.name)
      setIsOpen(true)
    };
  
    const [items, setItems] = React.useState([]);
    const [isOpen, setIsOpen] = React.useState(false);
    const [nameImage, setNameImage] = React.useState('');
    const [codeImage, setCodeImage] = React.useState('');
  
    function getBase64(file) {
      var reader = new FileReader();
      reader.readAsDataURL(file);
      reader.onload = function () {
        setCodeImage(reader.result)
      };
      reader.onerror = function (error) {
        console.log('Error: ', error);
      };
    }
  
    React.useEffect(() => {
      return console.log(items[0]['file'])
    }, [items]);
  
  
    return (
      <>
        <File
          name="image"
          label="Upload de imagens"
          onChange={handleChange}
          required={true}
          multiple={true}
        >
          {items.map((item, index) => (
            <File.Item {...item} key={index} />
          ))}
        </File>
  
        <Modal
          title={nameImage}
          onClose={() => setIsOpen(false)}
          show={isOpen}
        >
          <img src={codeImage} alt='Imagem' className='image' />
        </Modal>
      </>
    );
  }

Can we have your component code ?

Omar Sy
– Omar Sy

2020-07-28 20:07:10 +00:00
Commented Jul 28, 2020 at 20:07 — Omar Sy
– Omar Sy, Commented Jul 28, 2020 at 20:07
I put the code in the body of the question

Leticia Fatima
– Leticia Fatima

2020-07-28 20:09:42 +00:00
Commented Jul 28, 2020 at 20:09 — Leticia Fatima
– Leticia Fatima, Commented Jul 28, 2020 at 20:09

Çağatay Sel · Accepted Answer · 2020-07-28 20:18:05Z

2

When you first initialize items, it is an empty array so trying to log items[0].file will give error. Add undefined check. Also do not return it from useEffect. Return in useEffect is used for cleanup logic.

React.useEffect(() => {
 if(items[0] {
  console.log(items[0]['file'])
 }

}, [items]);

edited Jul 28, 2020 at 20:18

answered Jul 28, 2020 at 20:12

Çağatay Sel

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4 Comments

BARNOWL Over a year ago

Just curious, how can you make this dynamic without the use of [0] ?

Çağatay Sel Over a year ago

What do you mean by dynamic?

BARNOWL Over a year ago

suppose if op wanted to use index opposed to using [0] hardcoded? how would you go about finding the index key

Çağatay Sel Over a year ago

This check was added to avoid the initial empty state. If you want to check for any random index you can store the index in the state and check for items[state.myDynamicIndex]

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