---
sidebar_label: Page.waitForFunction
---
# Page.waitForFunction() method
Waits for a function to finish evaluating in the page's context.
**Signature:**
```typescript
class Page {
waitForFunction<
Params extends unknown[],
Func extends EvaluateFunc<Params> = EvaluateFunc<Params>
>(
pageFunction: Func | string,
options?: {
timeout?: number;
polling?: string | number;
},
...args: Params
): Promise<HandleFor<Awaited<ReturnType<Func>>>>;
}
```
## Parameters
| Parameter | Type | Description |
| ------------ | ------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| pageFunction | Func \| string | Function to be evaluated in browser context |
| options | { timeout?: number; polling?: string \| number; } | <i>(Optional)</i> Optional waiting parameters - <code>polling</code> - An interval at which the <code>pageFunction</code> is executed, defaults to <code>raf</code>. If <code>polling</code> is a number, then it is treated as an interval in milliseconds at which the function would be executed. If polling is a string, then it can be one of the following values: - <code>raf</code> - to constantly execute <code>pageFunction</code> in <code>requestAnimationFrame</code> callback. This is the tightest polling mode which is suitable to observe styling changes. - <code>mutation</code>- to execute pageFunction on every DOM mutation. - <code>timeout</code> - maximum time to wait for in milliseconds. Defaults to <code>30000</code> (30 seconds). Pass <code>0</code> to disable timeout. The default value can be changed by using the [Page.setDefaultTimeout()](./puppeteer.page.setdefaulttimeout.md) method. |
| args | Params | Arguments to pass to <code>pageFunction</code> |
**Returns:**
Promise<[HandleFor](./puppeteer.handlefor.md)<Awaited<ReturnType<Func>>>>
A `Promise` which resolves to a JSHandle/ElementHandle of the the `pageFunction`'s return value.
## Example 1
The [Page.waitForFunction()](./puppeteer.page.waitforfunction.md) can be used to observe viewport size change:
```ts
const puppeteer = require('puppeteer');
(async () => {
const browser = await puppeteer.launch();
const page = await browser.newPage();
const watchDog = page.waitForFunction('window.innerWidth < 100');
await page.setViewport({width: 50, height: 50});
await watchDog;
await browser.close();
})();
```
## Example 2
To pass arguments from node.js to the predicate of [Page.waitForFunction()](./puppeteer.page.waitforfunction.md) function:
```ts
const selector = '.foo';
await page.waitForFunction(
selector => !!document.querySelector(selector),
{},
selector
);
```
## Example 3
The predicate of [Page.waitForFunction()](./puppeteer.page.waitforfunction.md) can be asynchronous too:
```ts
const username = 'github-username';
await page.waitForFunction(
async username => {
const githubResponse = await fetch(
`https://api.github.com/users/${username}`
);
const githubUser = await githubResponse.json();
// show the avatar
const img = document.createElement('img');
img.src = githubUser.avatar_url;
// wait 3 seconds
await new Promise((resolve, reject) => setTimeout(resolve, 3000));
img.remove();
},
{},
username
);
```