How to map out preloaded images from an array in react?

Question

I am trying to preload some images for an image carousel and store them in an array. I seem to have everything working so far except when I try to map the images in the array in to JSX I get an error.

Error: Objects are not valid as a React child (found: [object HTMLImageElement]). If you meant to render a collection of children, use an array instead

Can someone tell me why please?

As a follow up question, my setInterval (which will be used to rotate through the images) isn't starting and I can't work out why so any help with that would be greatly appreciated.

import React, { useEffect, useState } from 'react'
import { CSSTransition } from 'react-transition-group'
import { ImageCarouselContainer, ImageCarouselSlide } from './imagecarousel.styles'
const images = [
      'https://images.unsplash.com/photo-1588392382834-a891154bca4d?ixlib=rb-1.2.1&ixid=eyJhcHBfaWQiOjEyMDd9&auto=format&fit=crop&w=2555&q=80',
      'https://images.unsplash.com/photo-1441974231531-c6227db76b6e?ixlib=rb-1.2.1&ixid=eyJhcHBfaWQiOjEyMDd9&auto=format&fit=crop&w=2551&q=80',
      'https://images.unsplash.com/photo-1470813740244-df37b8c1edcb?ixlib=rb-1.2.1&ixid=eyJhcHBfaWQiOjEyMDd9&auto=format&fit=crop&w=2551&q=80'
]

const ImageCarousel = () => {
      const [activeImage, setActiveImage] = useState(1);
      const [imagesArr, setImagesArr] = useState([])
      
      useEffect(() => {
            let loadedImages = []
            images.forEach(el => {
                  let img = new Image()
                  img.onload = () => {
                        loadedImages.push(img);
                  }
                  img.src = el
            })
            setImagesArr(loadedImages);
            const counter = () => {
                  if(activeImage < imagesArr.length) {
                        setActiveImage(activeImage + 1)
                  } else {
                        setActiveImage(0) 
                  }
            }
            
            const interval = setInterval(counter, 1000)
            
            return () => {
                  clearInterval(interval);
            }
            
      }, [])

      return (
            <ImageCarouselContainer>

                  {      
                        imagesArr &&
                        imagesArr.map((el, idx) => (
                        <CSSTransition
                              classNames='image'
                              timeout={1000}
                              key={idx}
                              in={activeImage === idx ? true : false}
                              unmountOnExit
                        >
                              <ImageCarouselSlide 
                                    
                              >
                              {el}
                              </ImageCarouselSlide>
                        </CSSTransition>  
                        ))
                  }

            </ImageCarouselContainer>
      )
}

export default ImageCarousel

Sorry, its: Error: Objects are not valid as a React child (found: [object HTMLImageElement]). If you meant to render a collection of children, use an array instead. — mattavero
– mattavero, Commented Oct 22, 2020 at 11:53
el is an Image object. So, {el} is probably throwing an error? — adiga
– adiga, Commented Oct 22, 2020 at 11:58

Robert · Accepted Answer · 2020-10-22 11:59:17Z

1

you try to put pure html object not react component to render function. so it dosn't has props etc...

change

            images.forEach(el => {
                  let img = new Image()
                  img.onload = () => {
                        loadedImages.push(img);
                  }
                  img.src = el
            }

to

            images.forEach(el => {
                  let img = new Image()
                  img.onload = () => {
                        loadedImages.push(<img src={el}>); 
                  }
                  img.src = el
            }

answered Oct 22, 2020 at 11:59

Robert

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