[Home](./index.md) > [puppeteer](./puppeteer.md) > [WebWorker](./puppeteer.webworker.md)
## 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
```
## 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
```js
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());
}
```
## Properties
| Property | Modifiers | Type | Description |
| --- | --- | --- | --- |
| [\_client](./puppeteer.webworker._client.md) | | [CDPSession](./puppeteer.cdpsession.md) | |
| [\_executionContextCallback](./puppeteer.webworker._executioncontextcallback.md) | | (value: [ExecutionContext](./puppeteer.executioncontext.md)) => void | |
| [\_executionContextPromise](./puppeteer.webworker._executioncontextpromise.md) | | Promise<[ExecutionContext](./puppeteer.executioncontext.md)> | |
| [\_url](./puppeteer.webworker._url.md) | | string | |
## 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 \[(await worker.executionContext()).evaluateHandle(pageFunction, ...args)\](\#executioncontextevaluatehandlepagefunction-args). |
| [executionContext()](./puppeteer.webworker.executioncontext.md) | | Returns the ExecutionContext the WebWorker runs in |
| [url()](./puppeteer.webworker.url.md) | | |