addImgToJsons.js

const fs = require('fs');
const path = require('path');

// here i have 10k json files delivered by collection owner
const dirPath = '/Users/user/Documents/collection_V1/json';

const updateContent = (filePath, content) => {
  const match = filePath.match(/(\d+)\.json$/);
  if (match) {
    console.log(match[1]); // get tokenId from path
    content.image = `ipfs://{directoryWithImages/${match[1]}.jpg` // upload all images to IPFS first
  }
  return content;
};

fs.readdir(dirPath, (err, files) => {
  if (err) {
    console.error("Could not list the directory.", err);
    process.exit(1);
  }

  files.forEach((file, index) => {
    if (path.extname(file) === '.json') {
      const filePath = path.join(dirPath, file);

      fs.readFile(filePath, 'utf8', (err, data) => {
        if (err) {
          console.error(`Error reading file from disk: ${err}`);
        } else {
          // parse JSON string to JSON object
          const jsonData = JSON.parse(data);

          // update content of JSON object
          const updatedData = updateContent(filePath, jsonData);

          // write updated content back to file
          fs.writeFile(filePath, JSON.stringify(updatedData, null, 2), (err) => {
            if (err) {
              console.error(`Error writing file on disk: ${err}`);
            }
          });
        }
      });
    }
  });
});