A method to incrementally download large compressed files in a web browser while simultaneously decompressing and saving them to your computer.

browser-gzip-csv-downloader-decompressor.js

// Add click event listener to a button
document.querySelector('button').addEventListener('click', async () => {
  try {
    const filename = 'sample.csv.gz';

    // Open a file picker dialog and get a handle to the file
    const fileHandle = await window.showSaveFilePicker({
      suggestedName: filename.slice(0, -'.csv.gz'.length), // Remove .csv.gz extension
      types: [
        {
          description: 'CSV File',
          accept: { 'text/csv': ['.csv'] },
        },
      ],
    });

    // Fetch the compressed file
    const response = await fetch('sample.csv.gz');

    // Process the file: decompress, decode, and save
    await response.body
      .pipeThrough(new DecompressionStream('gzip')) // Decompress the gzip stream
      .pipeThrough(new TextDecoderStream()) // Decode the decompressed stream to text
      .pipeTo(await fileHandle.createWritable()); // Write the decoded text to the file

    console.log('File downloaded and saved successfully');
  } catch (error) {
    console.error('Error downloading or saving file:', error);
  }
});