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React Assets

Using import to load assets

We've seen that we can import TypeScript code into the current file/module. We've also seen that we can import JSON data from a file into a variable.

The fact that our development tools give us various loaders to deal with importing various data is very helpful.

What can we import?

Our development and build tools come with various loaders to be able to import various data types. If there is a type of data we need to support we can either find an existing loader and add it to our project or we can write our own since a loader is nothing more than some TypeScript (or JavaScript) code that describes how to read the file and provide a JavaScript object in response.

  • TypeScript code
  • JSON
  • Images
  • Fonts
  • CSS

Importing images in a React application

Your first inclination to deal with images in JSX will be to write code like the following:

<img src="../images/my-awesome-image.png" alt="Awesomeness Defined" />

However, you will find that this doesn't work in development or in production.

The correct method is to import the image first:

import image from '../my-awesome-image.png'

This provides you a string containing the path to the image to use in code.

return <img src={image}/>
}

Why do we import images?

This seems like a big difference to how we dealt with images in plain HTML and CSS projects. We use this method in our React (and other TypeScript/JavaScript projects) so that our build tool can add these features:

  1. It ensures that the file name for the image is "slugged". Slugging means that it takes some unique value and makes that part of the image path. You'll notice that the string in image isn't just my-awesome-image.png but something like my-awesome-image-dea415f.png (and maybe even a longer string). That bit of text after the file name is the "checksum" of the file. The checksum is a value that changes any time the contents of the file change. We do this because we'd like to cache the images for a long time on our client's browsers. By having a checksum we can set a long caching time but ensure that the client fetches a fresh image when we change the contents. Since the image will have a new file name when the contents change, we achieve both caching and freshness.
  2. It also allows the deploy process to only upload the images that are used in the code. Unused images won't have an import and thus won't be included in the deployment to our hosting system.
  3. Some loaders will do image optimizations to ensure the file is as small as possible.
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