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2022-08-13 18:01:26 -04:00

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Headless Automation

Headless automation involves controlling "headless browsers" to access websites and submit or download data. It is also possible to automate browsers using custom browser extensions.

The SheetJS standalone script can be added to any website by inserting a SCRIPT tag. Headless browsers usually provide utility functions for running custom snippets in the browser and passing data back to the automation script.

Use Case

This demo focuses on exporting table data to a workbook. Headless browsers do not generally support passing objects between the browser context and the automation script, so the file data must be generated in the browser context and sent back to the automation script for saving in the filesystem. Steps:

Launch the headless browser and load the target webpage.
Add the standalone SheetJS build to the page in a SCRIPT tag.
Add a script to the page (in the browser context) that will:

Make a workbook object from the first table using XLSX.utils.table_to_book
Generate the bytes for an XLSB file using XLSX.write
Send the bytes back to the automation script

When the automation context receives data, save to a file

This demo exports data from https://sheetjs.com/demos/table.

:::note

It is also possible to parse files from the browser context, but parsing from the automation context is more performant and strongly recommended.

:::

Puppeteer

Puppeteer enables headless Chromium automation for NodeJS. Releases ship with an installer script. Installation is straightforward:

npm i https://cdn.sheetjs.com/xlsx-latest/xlsx-latest.tgz puppeteer

Binary strings are the favored data type. They can be safely passed from the browser context to the automation script. NodeJS provides an API to write binary strings to file (fs.writeFileSync using encoding binary).

To run the example, after installing the packages, save the following script to SheetJSPuppeteer.js and run node SheetJSPuppeteer.js. Steps are commented:

const fs = require("fs");
const puppeteer = require('puppeteer');
(async () => {
  /* (1) Load the target page */
  const browser = await puppeteer.launch();
  const page = await browser.newPage();
  page.on("console", msg => console.log("PAGE LOG:", msg.text()));
  await page.setViewport({width: 1920, height: 1080});
  await page.goto('https://sheetjs.com/demos/table');

  /* (2) Load the standalone SheetJS build from the CDN */
  await page.addScriptTag({ url: 'https://cdn.sheetjs.com/xlsx-latest/package/dist/xlsx.full.min.js' });

  /* (3) Run the snippet in browser and return data */
  const bin = await page.evaluate(() => {
    /* NOTE: this function will be evaluated in the browser context.
       `page`, `fs` and `puppeteer` are not available.
       `XLSX` will be available thanks to step 2 */

    /* find first table */
    var table = document.body.getElementsByTagName('table')[0];

    /* call table_to_book on first table */
    var wb = XLSX.utils.table_to_book(table);

    /* generate XLSB and return binary string */
    return XLSX.write(wb, {type: "binary", bookType: "xlsb"});
  });

  /* (4) write data to file */
  fs.writeFileSync("SheetJSPuppeteer.xlsb", bin, { encoding: "binary" });

  await browser.close();
})();

Playwright

Playwright presents a unified scripting framework for Chromium, WebKit, and other browsers. It draws inspiration from Puppeteer. In fact, the example code is almost identical!

npm i https://cdn.sheetjs.com/xlsx-latest/xlsx-latest.tgz playwright

To run the example, after installing the packages, save the following script to SheetJSPlaywright.js and run node SheetJSPlaywright.js. Import divergences from the Puppeteer example are highlighted below:

const fs = require("fs");
// highlight-next-line
const { webkit } = require('playwright'); // import desired browser
(async () => {
  /* (1) Load the target page */
  // highlight-next-line
  const browser = await webkit.launch(); // launch desired browser
  const page = await browser.newPage();
  page.on("console", msg => console.log("PAGE LOG:", msg.text()));
  // highlight-next-line
  await page.setViewportSize({width: 1920, height: 1080}); // different name :(
  await page.goto('https://sheetjs.com/demos/table');

  /* (2) Load the standalone SheetJS build from the CDN */
  await page.addScriptTag({ url: 'https://cdn.sheetjs.com/xlsx-latest/package/dist/xlsx.full.min.js' });

  /* (3) Run the snippet in browser and return data */
  const bin = await page.evaluate(() => {
    /* NOTE: this function will be evaluated in the browser context.
       `page`, `fs` and the browser engine are not available.
       `XLSX` will be available thanks to step 2 */

    /* find first table */
    var table = document.body.getElementsByTagName('table')[0];

    /* call table_to_book on first table */
    var wb = XLSX.utils.table_to_book(table);

    /* generate XLSB and return binary string */
    return XLSX.write(wb, {type: "binary", bookType: "xlsb"});
  });

  /* (4) write data to file */
  fs.writeFileSync("SheetJSPlaywright.xlsb", bin, { encoding: "binary" });

  await browser.close();
})();

PhantomJS

PhantomJS is a headless web browser powered by WebKit. Standalone binaries are available at https://phantomjs.org/download.html

:::warning

This information is provided for legacy deployments. PhantomJS development has been suspended and there are known vulnerabilities, so new projects should use alternatives. For WebKit automation, new projects should use Playwright.

:::

Binary strings are the favored data type. They can be safely passed from the browser context to the automation script. PhantomJS provides an API to write binary strings to file (fs.write using mode wb).

To run the example, save the following script to SheetJSPhantom.js in the same folder as phantomjs.exe or phantomjs and run

./phantomjs SheetJSPhantom.js     ## macOS / Linux
.\phantomjs.exe SheetJSPhantom.js ## windows

The steps are marked in the comments:

var page = require('webpage').create();
page.onConsoleMessage = function(msg) { console.log(msg); };

/* (1) Load the target page */
page.open('https://sheetjs.com/demos/table', function() {

  /* (2) Load the standalone SheetJS build from the CDN */
  page.includeJs("https://cdn.sheetjs.com/xlsx-latest/package/dist/xlsx.full.min.js", function() {

    /* (3) Run the snippet in browser and return data */
    var bin = page.evaluateJavaScript([ "function(){",

      /* find first table */
      "var table = document.body.getElementsByTagName('table')[0];",

      /* call table_to_book on first table */
      "var wb = XLSX.utils.table_to_book(table);",

      /* generate XLSB file and return binary string */
      "return XLSX.write(wb, {type: 'binary', bookType: 'xlsb'});",
    "}" ].join(""));

    /* (4) write data to file */
    require("fs").write("SheetJSPhantomJS.xlsb", bin, "wb");

    phantom.exit();
  });
});

:::caution

PhantomJS is very finicky and will hang if there are script errors. It is strongly recommended to add verbose logging and to lint scripts before use.

:::

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