Create a json file from a html form

I have a html form and I want to create a json-file with data introduced in html fields.
Right now, it is visible in console json-text but it doesn’t create a new json-file with this content.
Also,I have an error, Uncaught ReferenceError: require is not defined.

    // get the form element from dom
    const formElement = document.querySelector('form#forms')

    // convert the form to JSON
    const getFormJSON = (form) => {
      const data = new FormData(form);
      return Array.from(data.keys()).reduce((result, key) => {
        if (result[key]) {
          result[key] = data.getAll(key)
          return result
        }
        result[key] = data.get(key);
        return result;
      }, {});
    };

    // handle the form submission event, prevent default form behaviour, check validity, convert form to JSON
    const handler = (event) => {
      event.preventDefault();
      const valid = formElement.reportValidity();
      if (valid) {
        const result = getFormJSON(formElement);
        // handle one, multiple or no files uploaded
        const images = [result.images].flat().filter((file) => !!file.name)
        // handle one, multiple or no languages selected
        const languages = [result.languages || []].flat();
        // convert the checkbox to a boolean
        const isHappyReader = !!(result.isHappyReader && result.isHappyReader === 'on')

        // use spread function, but override the keys we've made changes to
        const output = {
          ...result,
          images,
          languages,
          isHappyReader
        }
        console.log(output)
      }
    }

    formElement.addEventListener("submit", handler)



    const fs = require('fs');
    const dataNew = JSON.stringify(output);
    fs.writeFile('output.json', dataNew, (err) => {
    if (err) {
        console.log("error")
        throw err;
    }
    console.log("JSON data is saved.");
});
  </script>
</body>

Answer

It seems you are on the frontend. You can’t write files like this because of security. This would result in every website with some JavaScript being potentially able to write files to your system and you really don’t want that. Additionally fs is a Node API that is not available in the browser.

One option would be to download the JSON file from the frontend which you could do using the following code:

/**
 * Download a JSON file.
 * @param {sting} filename filename
 * @param {any} obj any serializeable object
 */
function downloadJson(filename, obj) {
  // serialize to JSON and pretty print with indent of 4
  const text = JSON.stringify(obj, null, 4);

  // create anchor tag
  var element = document.createElement("a");
  element.setAttribute(
    "href",
    "data:application/json;charset=utf-8," + encodeURIComponent(text)
  );
  element.setAttribute("download", filename);
  // don't display the tag
  element.style.display = "none";
  // add tag to document
  document.body.appendChild(element);
  // click it: this starts the download
  element.click();
  // remove the tag again
  document.body.removeChild(element);
}

window.addEventListener("DOMContentLoaded", (event) => {
  // Start file download.
  downloadJson("helloWorld.json", { hello: "World" });
});

If you add that to your page the save dialog will appear on a user’s system. Here the one I am getting on Ubuntu:

And here the content of the downloaded file:

Please read this thread on the pros and cons of using an approach like this.