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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.

def handle_worker(worker):
    print("worker created: " + worker.url)
    worker.on("close", lambda: print("worker destroyed: " + worker.url))

page.on('worker', handle_worker)

print("current workers:")
for worker in page.workers:
    print("    " + worker.url)

Methods​

evaluate​

Added before v1.9 worker.evaluate

Returns the return value of expression.

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() returns undefined. Playwright also supports transferring some additional values that are not serializable by JSON: -0, NaN, Infinity, -Infinity.

Usage

worker.evaluate(expression)
worker.evaluate(expression, **kwargs)

Arguments

  • expression str#

    JavaScript expression to be evaluated in the browser context. If the expression evaluates to a function, the function is automatically invoked.

  • arg EvaluationArgument (optional)#

    Optional argument to pass to expression.

Returns

evaluate_handle​

Added before v1.9 worker.evaluate_handle

Returns the return value of expression as a JSHandle.

The only difference between worker.evaluate() and worker.evaluate_handle() is that worker.evaluate_handle() returns JSHandle.

If the function passed to the worker.evaluate_handle() returns a Promise, then worker.evaluate_handle() would wait for the promise to resolve and return its value.

Usage

worker.evaluate_handle(expression)
worker.evaluate_handle(expression, **kwargs)

Arguments

  • expression str#

    JavaScript expression to be evaluated in the browser context. If the expression evaluates to a function, the function is automatically invoked.

  • arg EvaluationArgument (optional)#

    Optional argument to pass to expression.

Returns

Properties​

url​

Added before v1.9 worker.url

Usage

worker.url

Returns

Events​

on("close")​

Added before v1.9 worker.on("close")

Emitted when this dedicated WebWorker is terminated.

Usage

worker.on("close", handler)

Event data