[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 ``` 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 ```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) | | [executionContext()](./puppeteer.webworker.executioncontext.md) | | Returns the ExecutionContext the WebWorker runs in | | [url()](./puppeteer.webworker.url.md) | | |