Overriding showOpenFilePicker with Puppeteer

Question

As illustrated in here here, Puppeteer allows to override Javascript functions. I want to override showOpenFilePicker function. That is, when the showOpenFilePicker invoked by the web page. I want to run another function before the showOpenFilePicker.

const puppeteer = require("puppeteer");

(async () => {
  const browser = await puppeteer.launch({ headless: false });
  const page = await browser.newPage();

  await page.evaluateOnNewDocument(() => {
    Object.defineProperty(HTMLCanvasElement.prototype, "toBlob", {
      value: () => {
        console.log("Hey there");
      },
    });
  });

  await page.goto("https://example.com");

  await page.evaluate(() => {
    console.log(HTMLCanvasElement.prototype.toBlob.toString());
  });

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

Answer 1

You can override built-in functions in Puppeteer like in the code sample below. This replaces the original function with an override that logs the arguments to the console.

const puppeteer = require("puppeteer");

(async () => {
  const browser = await puppeteer.launch({ headless: false });
  const page = await browser.newPage();

  await page.evaluateOnNewDocument(() => {
    const originalShowOpenFilePicker = window.showOpenFilePicker;
    window.showOpenFilePicker = (...args) => {
      console.log('Modified `showOpenFilePicker` called with these arguments:', args);
      return originalShowOpenFilePicker(...args);
    };
  });

  await page.goto("https://example.com");

  await page.evaluate(() => {
    console.log(showOpenFilePicker());
  });

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