Wails

The NodeJS Module can be imported from JavaScript code.

The "Complete Example" creates an app that looks like the screenshot:

macOS	Linux

Native Modules

All operations must be run from Go code. This example passes Base64 strings.

caution

Wails currently does not provide the equivalent of NodeJS fs module. All raw file operations must be performed in Go code.

The HTML File Input Element does not show a file picker. This is a known bug. The demo works around the issue by showing pickers in Go code.

Reading Files

The file picker and reading operations can be combined in one Go function.

Go

import (
  "context"
  "encoding/base64"
  "io/ioutil"
  "github.com/wailsapp/wails/v2/pkg/runtime"
)

type App struct {
  ctx context.Context
}

// ReadFile shows an open file dialog and returns the data as Base64 string
func (a *App) ReadFile() string {
  selection, err := runtime.OpenFileDialog(a.ctx, runtime.OpenDialogOptions{
    Title: "Select File",
    Filters: []runtime.FileFilter{
      { DisplayName: "Excel Workbooks (*.xlsx)", Pattern: "*.xlsx", },
      // ... more filters for more file types
    },
  })
  if err != nil { return "" } // The demo app shows an error message
  data, err := ioutil.ReadFile(selection)
  if err != nil { return "" } // The demo app shows an error message
  return base64.StdEncoding.EncodeToString(data)
}

JS

Wails will automatically create bindings for use in JS:

frontend/src/App.svelte

import { read, utils } from 'xlsx';
import { ReadFile } from '../wailsjs/go/main/App';

async function importFile(evt) {
  const b64 = await ReadFile();
  const wb = read(b64, { type: "base64" });
  const ws = wb.Sheets[wb.SheetNames[0]]; // get the first worksheet
  html = utils.sheet_to_html(ws); // generate HTML and update state
}

Writing Files

There is a multi-part dance since the library needs the file extension.

1) Show the save file picker in Go, pass back to JS

2) Generate the file data in JS, pass the data back to Go

3) Write to file in Go

Go

Two Go functions will be exposed.

• SaveFile will show the file picker and return the path:

import (
  "context"
  "github.com/wailsapp/wails/v2/pkg/runtime"
)

type App struct {
  ctx context.Context
}

func (a *App) SaveFile() string {
  selection, err := runtime.SaveFileDialog(a.ctx, runtime.SaveDialogOptions{
    Title: "Select File",
    DefaultFilename: "SheetJSWails.xlsx",
    Filters: []runtime.FileFilter{
      { DisplayName: "Excel Workbooks (*.xlsx)", Pattern: "*.xlsx", },
      // ... more filters for more file types
    },
  })
  if err != nil { return "" } // The demo app shows an error message
  return selection
}

• WriteFile performs the file write given a Base64 string and file path:

import (
  "context"
  "encoding/base64"
  "io/ioutil"
)

type App struct {
  ctx context.Context
}

func (a *App) WriteFile(b64 string, path string) {
  buf, _ := base64.StdEncoding.DecodeString(b64);
  _ = ioutil.WriteFile(path, buf, 0644);
}

JS

Wails will automatically create bindings for use in JS:

import { utils, write } from 'xlsx';
import { SaveFile, WriteFile } from '../wailsjs/go/main/App';

async function exportFile(wb) {
  /* generate workbook */
  const elt = tbl.getElementsByTagName("TABLE")[0];
  const wb = utils.table_to_book(elt);

  /* show save picker and get path */
  const path = await SaveFile();

  /* generate base64 string based on the path */
  const b64 = write(wb, { bookType: path.slice(path.lastIndexOf(".")+1), type: "base64" });

  /* write to file */
  await WriteFile(b64, path);
}

Complete Example

This demo was tested against Wails v2.3.1 on 2023 January 08 using the Svelte TypeScript starter.

0) Read Wails "Getting Started" guide and install dependencies.

1) Create a new Wails app:

wails init -n sheetjs-wails -t svelte-ts

2) Enter the directory:

cd sheetjs-wails

3) Install front-end dependencies:

cd frontend
curl -L -o src/assets/logo.png https://sheetjs.com/sketch1024.png
npm i --save https://cdn.sheetjs.com/xlsx-latest/xlsx-latest.tgz
cd ..

4) Download source files:

• Download app.go and replace app.go
• Download App.svelte and replace frontend/src/App.svelte

curl -L -o app.go https://docs.sheetjs.com/wails/app.go
curl -L -o frontend/src/App.svelte https://docs.sheetjs.com/wails/App.svelte

5) Build the app with

wails build

At the end, it will print the path to the generated program. Run the program!