puppeteer/website/versioned_docs/version-19.4.0/api/puppeteer.page.exposefunction.md

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Page.exposeFunction

Page.exposeFunction() method

The method adds a function called name on the page's window object. When called, the function executes puppeteerFunction in node.js and returns a Promise which resolves to the return value of puppeteerFunction.

If the puppeteerFunction returns a Promise, it will be awaited.

:::note

Functions installed via page.exposeFunction survive navigations.

:::note

Signature:

class Page {
  exposeFunction(
    name: string,
    pptrFunction:
      | Function
      | {
          default: Function;
        }
  ): Promise<void>;
}

Parameters

Parameter	Type	Description
name	string	Name of the function on the window object
pptrFunction	Function | { default: Function; }	Callback function which will be called in Puppeteer's context.

Returns:

Promise<void>

Example 1

An example of adding an md5 function into the page:

const puppeteer = require('puppeteer');
const crypto = require('crypto');

(async () => {
  const browser = await puppeteer.launch();
  const page = await browser.newPage();
  page.on('console', msg => console.log(msg.text()));
  await page.exposeFunction('md5', text =>
    crypto.createHash('md5').update(text).digest('hex')
  );
  await page.evaluate(async () => {
    // use window.md5 to compute hashes
    const myString = 'PUPPETEER';
    const myHash = await window.md5(myString);
    console.log(`md5 of ${myString} is ${myHash}`);
  });
  await browser.close();
})();

Example 2

An example of adding a window.readfile function into the page:

const puppeteer = require('puppeteer');
const fs = require('fs');

(async () => {
  const browser = await puppeteer.launch();
  const page = await browser.newPage();
  page.on('console', msg => console.log(msg.text()));
  await page.exposeFunction('readfile', async filePath => {
    return new Promise((resolve, reject) => {
      fs.readFile(filePath, 'utf8', (err, text) => {
        if (err) reject(err);
        else resolve(text);
      });
    });
  });
  await page.evaluate(async () => {
    // use window.readfile to read contents of a file
    const content = await window.readfile('/etc/hosts');
    console.log(content);
  });
  await browser.close();
})();