class: Worker

class: Worker

The Worker class represents a WebWorker. worker event is emitted on the page object to signal a worker creation. close event is emitted on the worker object when the worker is gone.

page.on('worker', worker => {
  console.log('Worker created: ' + worker.url());
  worker.on('close', worker => console.log('Worker destroyed: ' + worker.url()));
});

console.log('Current workers:');
for (const worker of page.workers())
  console.log('  ' + worker.url());
  • event: ‘close’
  • worker.evaluate(pageFunction[, arg])
  • worker.evaluateHandle(pageFunction[, arg])
  • worker.url()

event: ‘close’

  • <Worker>

Emitted when this dedicated WebWorker is terminated.

worker.evaluate(pageFunction[, arg])

  • pageFunction <function “Function”)|string ”String“)> Function to be evaluated in the worker context
  • arg <Serializable “Serializable”)|JSHandle> Optional argument to pass to pageFunction
  • returns: <Promise “Promise”)<Serializable ”Serializable“)>> Promise which resolves to the return value of pageFunction

If the function passed to the worker.evaluate returns a Promise “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 “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.

worker.evaluateHandle(pageFunction[, arg])

  • pageFunction <function “Function”)|string ”String“)> Function to be evaluated in the page context
  • arg <Serializable “Serializable”)|JSHandle> Optional argument to pass to pageFunction
  • returns: <Promise “Promise”)<JSHandle>> Promise which resolves to the return value of pageFunction as in-page object (JSHandle)

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 “Promise”), then worker.evaluateHandle would wait for the promise to resolve and return its value.

worker.url()

  • returns: <string “String”)>