next-image-export-optimizer
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1.12.3 • Public • Published

Next-Image-Export-Optimizer

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Use Next.js advanced <Image/> component with the static export functionality. Optimizes all static images in an additional step after the Next.js static export.

  • Reduces the image size and page load times drastically through responsive images
  • Fast image transformation using sharp.js (also used by the Next.js server in production)
  • Conversion of JPEG and PNG files to the modern WEBP format by default
  • Serve the exported React bundle only via a CDN. No server required
  • Automatic generation of tiny, blurry placeholder images
  • Minimal configuration necessary
  • Supports TypeScript
  • Supports remote images which will be downloaded and optimized
  • Supports animated images (accepted formats: GIF and WEBP)
  • Note that only one global value can be used for the image quality setting. The default value is 75.

Placement of the images:

  • All images that should be optimized are stored inside the public folder like public/images (except for the statically imported images and remote images). The images are then referenced in the src attribute of the <ExportedImage /> component.

Installation

npm install next-image-export-optimizer

# Or
yarn add next-image-export-optimizer
pnpm install next-image-export-optimizer

Configure the library in your Next.js configuration file:

// next.config.js
module.exports = {
  output: "export",
  images: {
    loader: "custom",
    imageSizes: [16, 32, 48, 64, 96, 128, 256, 384],
    deviceSizes: [640, 750, 828, 1080, 1200, 1920, 2048, 3840],
  },
  transpilePackages: ["next-image-export-optimizer"],
  env: {
    nextImageExportOptimizer_imageFolderPath: "public/images",
    nextImageExportOptimizer_exportFolderPath: "out",
    nextImageExportOptimizer_quality: "75",
    nextImageExportOptimizer_storePicturesInWEBP: "true",
    nextImageExportOptimizer_exportFolderName: "nextImageExportOptimizer",

    // If you do not want to use blurry placeholder images, then you can set
    // nextImageExportOptimizer_generateAndUseBlurImages to false and pass
    // `placeholder="empty"` to all <ExportedImage> components.
    nextImageExportOptimizer_generateAndUseBlurImages: "true",

    // If you want to cache the remote images, you can set the time to live of the cache in seconds.
    // The default value is 0 seconds.
    nextImageExportOptimizer_remoteImageCacheTTL: "0",
  },
};
  1. Add the above configuration to your next.config.js

  2. Change the default values in your next.config.js where appropriate. For example, specify the folder where all the images are stored (Defaults to public/images)

  3. Change the export command in package.json

    {
    -  "export": "next build",
    +  "export": "next build && next-image-export-optimizer"
    }

    If your Next.js project is not at the root directory where you are running the commands, for example if you are using a monorepo, you can specify the location of the next.config.js as an argument to the script:

    "export": "next build && next-image-export-optimizer --nextConfigPath path/to/my/next.config.js"

    If you want to specify the path to the output folder, you can either do so by setting the nextImageExportOptimizer_exportFolderPath environment variable in your next.config.js file or by passing the --exportFolderPath argument to the script:

     "export": "next build && next-image-export-optimizer --exportFolderPath path/to/my/export/folder"
  4. Change the <Image /> component to the <ExportedImage /> component of this library.

    Example:

    // Old
    import Image from "next/image";
    
    <Image
      src="images/VERY_LARGE_IMAGE.jpg"
      alt="Large Image"
      width={500}
      height={500}
    />;
    
    // Replace with either of the following:
    
    // With static import (Recommended)
    import ExportedImage from "next-image-export-optimizer";
    import testPictureStatic from "PATH_TO_IMAGE/test_static.jpg";
    
    <ExportedImage src={testPictureStatic} alt="Static Image" />;
    
    // With dynamic import
    import ExportedImage from "next-image-export-optimizer";
    
    <ExportedImage
      src="images/VERY_LARGE_IMAGE.jpg"
      alt="Large Image"
      width={500}
      height={500}
    />;

    The static import method is recommended as it informs the client about the original image size. For image sizes larger than the original width, the next largest image size in the deviceSizes array (specified in the next.config.js) will be used for the generation of the srcset attribute.

    For the dynamic import method, this library will create duplicates of the original image for each image size in the deviceSizes array that is larger than the original image size.

  5. In the development mode, either the original image will be served as a fallback when the optimized images are not yet generated or the optimized image once the image transformation was executed for the specific image. The optimized images are created at build time only. In the exported, static React app, the responsive images are available as srcset and dynamically loaded by the browser.

  6. This library also supports remote images. You have to specify the src as a string starting with either http or https in the ExportedImage component.

    import ExportedImage from "next-image-export-optimizer";
    
    <ExportedImage
      src="https://example.com/remote-image.jpg"
      alt="Remote Image"
      fill
      style={{ objectFit: "cover" }}
      priority
    />;

    In order for the image optimization at build time to work correctly, you have to specify all remote image urls in a file called remoteOptimizedImages.js in the root directory of your project (where the next.config.js is stored as well). The file should export an array of strings containing the urls of the remote images. Returning a promise of such array is also supported.

    Example:

    // remoteOptimizedImages.js
    module.exports = [
      "https://example.com/image1.jpg",
      "https://example.com/image2.jpg",
      "https://example.com/image3.jpg",
      // ...
    ];
    // Or with a promise
    module.exports = new Promise((resolve) =>
      resolve([
        "https://example.com/image1.jpg",
        "https://example.com/image2.jpg",
        "https://example.com/image3.jpg",
        // ...
      ])
    );
    
    // Or with an async API call
    module.exports = fetch("https://example.com/api/images").catch((error) => {
      console.error(error);
      return []; // return an empty array in case of error
    });

    At build time, the images will be either downloaded or read from the cache. The image urls will be replaced with the optimized image urls in the Exported Image component.

    You can specify the time to live of the cache in seconds by setting the nextImageExportOptimizer_remoteImageCacheTTL environment variable in your next.config.js file. The default value is 0 seconds (as the image might have changed).

    Set it to:

    • 60 for 1 minute
    • 3600 for 1 hour
    • 86400 for 1 day
    • 604800 for 1 week
    • 2592000 for 1 month
    • 31536000 for 1 year
  7. You can output the original, unoptimized images using the unoptimized prop. Example:

    import ExportedImage from "next-image-export-optimizer";
    
    <ExportedImage
      src={testPictureStatic}
      alt="Original, unoptimized image"
      unoptimized={true}
    />;
  8. Overriding presets in next.config.js:

    Placeholder images: If you do not want the automatic generation of tiny, blurry placeholder images, set the nextImageExportOptimizer_generateAndUseBlurImages environment variable to false and set the placeholder prop from the <ExportedImage /> component to empty.

    Usage of the WEBP format: If you do not want to use the WEBP format, set the nextImageExportOptimizer_storePicturesInWEBP environment variable to false.

    Rename the export folder name: If you want to rename the export folder name, set the nextImageExportOptimizer_exportFolderPath environment variable to the desired folder name. The default is nextImageExportOptimizer.

  9. You can still use the legacy image component next/legacy/image:

    import ExportedImage from "next-image-export-optimizer/legacy/ExportedImage";
    
    import testPictureStatic from "PATH_TO_IMAGE/test_static.jpg";
    
    <ExportedImage src={testPictureStatic} alt="Static Image" layout="fixed" />;
  10. BasePath: You can set the basePath in the next.config.js file. This is useful if you want to deploy your app to a subfolder of your domain.

    module.exports = {
      basePath: "/subfolder",
    };

    The ExportedImage component has a basePath prop which you can use to pass the basePath to the component.

    import ExportedImage from "next-image-export-optimizer";
    import testPictureStatic from "PATH_TO_IMAGE/test_static.jpg";
    
    <ExportedImage
      src={testPictureStatic}
      alt="Static Image"
      basePath="/subfolder"
    />;
  11. Animated images: You can use .gif and animated .webp images. Next-image-export-optimizer will automatically optimize the animated images and generate the srcset for the different resolutions.

    If you set the variable nextImageExportOptimizer_storePicturesInWEBP to true, the animated images will be converted to .webp format which can reduce the file size significantly. Note that animated png images are not supported by this package.

Live example

You can see a live example of the use of this library at reactapp.dev/next-image-export-optimizer

How it works

The <ExportedImage /> component of this library wraps around the <Image /> component of Next.js. Using the custom loader feature, it generates a srcset for different resolutions of the original image. The browser can then load the correct size based on the current viewport size.

In the development mode, the <ExportedImage /> component falls back to the original image if the optimized images are not yet generated. In the exported, static React app, the responsive images are available as srcset and dynamically loaded by the browser.

All images in the specified folder, as well as all statically imported images will be optimized and reduced versions will be created based on the requested widths.

The image transformation operation is optimized as it uses hashes to determine whether an image has already been optimized or not.

Warning Version 1.0.0 is a breaking change. It follows the changes introduced in Next 13.0.0 which replaces the next/image component with next/future/image. If you are using Next 12 or below, please use version 0.17.1.

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