code: function resizeImage(successCallback, errorCallback, file, targetWidth, targetHeight, encodingType) {
      var tempPhotoFileName = "";
      var targetContentType = "";
  
      if (encodingType == Camera.EncodingType.PNG) {
          tempPhotoFileName = "camera_cordova_temp_return.png";
          targetContentType = "image/png";
      } else {
          tempPhotoFileName = "camera_cordova_temp_return.jpg";
          targetContentType = "image/jpeg";
      }
  
      var storageFolder = getAppData().localFolder;
      file.copyAsync(storageFolder, file.name, Windows.Storage.NameCollisionOption.replaceExisting)
          .then(function (storageFile) {
              return fileIO.readBufferAsync(storageFile);
          })
          .then(function(buffer) {
              var strBase64 = encodeToBase64String(buffer);
              var imageData = "data:" + file.contentType + ";base64," + strBase64;
              var image = new Image();
              image.src = imageData;
              image.onload = function() {
                  var ratio = Math.min(targetWidth / this.width, targetHeight / this.height);
                  var imageWidth = ratio * this.width;
                  var imageHeight = ratio * this.height;
  
                  var canvas = document.createElement('canvas');
                  var storageFileName;
  
                  canvas.width = imageWidth;
                  canvas.height = imageHeight;
  
                  canvas.getContext("2d").drawImage(this, 0, 0, imageWidth, imageHeight);
  
                  var fileContent = canvas.toDataURL(targetContentType).split(',')[1];
  
                  var storageFolder = getAppData().localFolder;
  
                  storageFolder.createFileAsync(tempPhotoFileName, OptUnique)
                      .then(function (storagefile) {
                          var content = Windows.Security.Cryptography.CryptographicBuffer.decodeFromBase64String(fileContent);
                          storageFileName = storagefile.name;
                          return fileIO.writeBufferAsync(storagefile, content);
                      })
                      .done(function () {
                          successCallback("ms-appdata:///local/" + storageFileName);
                      }, errorCallback);
              };
          })
          .done(null, function(err) {
              errorCallback(err);
          }
      );
  }
docs: Resize method