docs.sheetjs.com/docz/docs/03-demos/03-desktop/03-wails.md

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Wails	demos/mobile	demos/grid	3	summary Webview + Go Backend

import Tabs from '@theme/Tabs'; import TabItem from '@theme/TabItem';

The NodeJS Module can be imported from JavaScript code.

This demo was tested against Wails v2.0.0-beta.44.2 on 2022 August 31 using the Svelte TypeScript starter.

:::caution

Wails currently does not provide the equivalent of NodeJS fs module.

The HTML File Input Element does not show a file picker. This is a known bug.

All raw file operations must be performed in Go code.

:::

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

Complete Example (click to show)

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

5. Build the app with

wails build

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

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

Reading Files

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

Go

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

type App struct {
  ctx context.Context
}

// ReadFile shows an open file dialog and returns the data as Base64 string
func (a *App) ReadFile() string {
  // highlight-next-line
  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
  // highlight-next-line
  data, err := ioutil.ReadFile(selection)
  if err != nil { return "" } // The demo app shows an error message
  // highlight-next-line
  return base64.StdEncoding.EncodeToString(data)
}

JS

Wails will automatically create window.go.main.App.ReadFile for use in JS:

import { read, utils } from 'xlsx';

async function importFile(evt) {
// highlight-start
  const b64 = window['go']['main']['App']['ReadFile']();
  const wb = read(b64, { type: "base64" });
// highlight-end
  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"
// highlight-start
  "github.com/wailsapp/wails/v2/pkg/runtime"
// highlight-end
)

type App struct {
  ctx context.Context
}

func (a *App) SaveFile() string {
// highlight-next-line
  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"
// highlight-start
  "encoding/base64"
  "io/ioutil"
// highlight-end
)

type App struct {
  ctx context.Context
}

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

JS

Wails will automatically create bindings for use in JS:

import { utils, write } from 'xlsx';

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 window['go']['main']['App']['SaveFile']();

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

  /* write to file */
  await window['go']['main']['App']['WriteFile'](b64, path);
  // The demo shows a success message at this point
}