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How do I properly use the map function to get the index of the element in the array?

April 19, 2022

Hello I am trying to find the index of the element in an array using map so that eventually I can create a onClick function that will change the image based on that index.

However when I add index to my map function I then get an error stating that the img is not defined.

const currentIndex = 0;

const gallery = 
  product.images.length > 1 ? (
    <Grid gap={2} columns={5}>
      {product.images.map(img, index => (
        <GatsbyImage 
          image={img.gatsbyImageData}
          key={img.id}
          alt={product.title}
        />
      ))}
    </Grid>
  ) : null;

The above code displays a list of thumbnail size images. I would like to eventually be able to click on each image and have the larger image appear.

Code for the larger image is below.

<div>
  <GatsbyImage
    image={product.images[currentIndex].gatsbyImageData}
    alt={product.title}
  />
  {gallery}
</div>

>Solution :

Simple parenthesis fix:

const currentIndex = 0;

const gallery = 
  product.images.length > 1 ? (
    <Grid gap={2} columns={5}>
      {product.images.map((img, index) => (
        <GatsbyImage 
          image={img.gatsbyImageData}
          key={img.id}
          alt={product.title}
        />
      ))}
    </Grid>
  ) : null;

Make sure to not pass two values, but one value to Array.map: a function with its own optional parameter called ‘index’

Consider expanding your work to a function that you can just reference, to make life easier, and code more legible, like this:

const currentIndex = 0;

const mapper = (img, index) => (
  <GatsbyImage image={img.gatsbyImageData} key={img.id} alt={product.title} />
);

const gallery =
  product.images.length > 1 ? (
    <Grid gap={2} columns={5}>
      {product.images.map(mapper)}
    </Grid>
  ) : null;

See more here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map#syntax