tauri-workspace/tauri/examples/communication/dist/fs.js

var dirSelect = document.getElementById("dir");

function getDir() {
  return dirSelect.value ? parseInt(dir.value) : null;
}

function arrayBufferToBase64(buffer, callback) {
  var blob = new Blob([buffer], {
    type: "application/octet-binary",
  });
  var reader = new FileReader();
  reader.onload = function (evt) {
    var dataurl = evt.target.result;
    callback(dataurl.substr(dataurl.indexOf(",") + 1));
  };
  reader.readAsDataURL(blob);
}

var pathInput = document.getElementById("path-to-read");

addClickEnterHandler(document.getElementById("read"), pathInput, function () {
  var pathToRead = pathInput.value;
  var isFile = pathToRead.match(/\S+\.\S+$/g);
  var opts = {
    dir: getDir(),
  };
  var promise = isFile
    ? window.__TAURI__.fs.readBinaryFile(pathToRead, opts)
    : window.__TAURI__.fs.readDir(pathToRead, opts);
  promise
    .then(function (response) {
      if (isFile) {
        if (pathToRead.includes(".png") || pathToRead.includes(".jpg")) {
          arrayBufferToBase64(new Uint8Array(response), function (base64) {
            var src = "data:image/png;base64," + base64;
            registerResponse('<img src="' + src + '"></img>');
          });
        } else {
          var value = String.fromCharCode.apply(null, response);
          registerResponse(
            '<textarea id="file-response" style="height: 400px"></textarea><button id="file-save">Save</button>'
          );
          var fileInput = document.getElementById("file-response");
          fileInput.value = value;
          document
            .getElementById("file-save")
            .addEventListener("click", function () {
              window.__TAURI__.fs
                .writeFile(
                  {
                    file: pathToRead,
                    contents: fileInput.value,
                  },
                  {
                    dir: getDir(),
                  }
                )
                .catch(registerResponse);
            });
        }
      } else {
        registerResponse(response);
      }
    })
    .catch(registerResponse);
});