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Version: 21.6.0

WebWorker class

This class represents a WebWorker.


export declare class WebWorker extends EventEmitter<Record<EventType, unknown>>

Extends: EventEmitter<Record<EventType, unknown>>


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.


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());


clientreadonlyCDPSessionThe CDP session client the WebWorker belongs to.


evaluate(pageFunction, args)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)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)
url()The URL of this web worker.