Displaying image previews before uploading is a common requirement in modern web applications. The example above uses the FileReader API to achieve this entirely on the client side. When you select one or more image files, the script listens for changes to the file input. It then loops through each selected file, checks if the file is an image by inspecting its type property, and creates a new FileReader for each file.

The FileReader reads the file as a data URL using readAsDataURL. When the file has been read, the onload event fires, and the result is a base64-encoded data URL. This data URL is set as the src of a new img element, which is then added to the preview container in the DOM. Because the code uses a loop, it can handle multiple files at once, showing a preview for each selected image. This approach ensures you can view your images before uploading, without sending any data to the server.