---
sidebar_label: WebWorker
---
# WebWorker class
The WebWorker class represents a [WebWorker](https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API).
**Signature:**
```typescript
export declare class WebWorker extends EventEmitter
```
**Extends:** [EventEmitter](./puppeteer.eventemitter.md)
## Remarks
The events `workercreated` and `workerdestroyed` are emitted on the page object to signal the worker lifecycle.
The constructor for this class is marked as internal. Third-party code should not call the constructor directly or create subclasses that extend the `WebWorker` class.
## Example
```ts
page.on('workercreated', worker =>
console.log('Worker created: ' + worker.url())
);
page.on('workerdestroyed', worker =>
console.log('Worker destroyed: ' + worker.url())
);
console.log('Current workers:');
for (const worker of page.workers()) {
console.log(' ' + worker.url());
}
```
## Methods
| Method | Modifiers | Description |
| ----------------------------------------------------------------------------- | --------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| [evaluate(pageFunction, args)](./puppeteer.webworker.evaluate.md) | | If the function passed to the worker.evaluate returns a Promise, then worker.evaluate would wait for the promise to resolve and return its value. If the function passed to the worker.evaluate returns a non-serializable value, then worker.evaluate resolves to undefined. DevTools Protocol also supports transferring some additional values that are not serializable by JSON: -0, NaN, Infinity, -Infinity, and bigint literals. Shortcut for await worker.executionContext()).evaluate(pageFunction, ...args). |
| [evaluateHandle(pageFunction, args)](./puppeteer.webworker.evaluatehandle.md) | | The only difference between worker.evaluate and worker.evaluateHandle is that worker.evaluateHandle returns in-page object (JSHandle). If the function passed to the worker.evaluateHandle returns a Promise, then worker.evaluateHandle would wait for the promise to resolve and return its value. Shortcut for await worker.executionContext()).evaluateHandle(pageFunction, ...args) |
| [executionContext()](./puppeteer.webworker.executioncontext.md) | | Returns the ExecutionContext the WebWorker runs in |
| [url()](./puppeteer.webworker.url.md) | | |