puppeteer/docs/api/puppeteer.page.exposefunction.md

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---
sidebar_label: 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.
:::
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#### Signature:
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```typescript
class Page {
abstract exposeFunction(
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name: string,
pptrFunction:
| Function
| {
default: Function;
}
): Promise<void>;
}
```
## Parameters
<table><thead><tr><th>
Parameter
</th><th>
Type
</th><th>
Description
</th></tr></thead>
<tbody><tr><td>
name
</td><td>
string
</td><td>
Name of the function on the window object
</td></tr>
<tr><td>
pptrFunction
</td><td>
Function \| &#123; default: Function; &#125;
</td><td>
Callback function which will be called in Puppeteer's context.
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</td></tr>
</tbody></table>
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**Returns:**
Promise&lt;void&gt;
## Example 1
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An example of adding an `md5` function into the page:
```ts
import puppeteer from 'puppeteer';
import crypto from 'crypto';
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(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
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An example of adding a `window.readfile` function into the page:
```ts
import puppeteer from 'puppeteer';
import fs from 'fs';
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(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();
})();
```