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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

expect_event​

Added in: v1.57 worker.expect_event

Waits for event to fire and passes its value into the predicate function. Returns when the predicate returns truthy value. Will throw an error if the page is closed before the event is fired. Returns the event data value.

Usage

with worker.expect_event("console") as event_info:
    worker.evaluate("console.log(42)")
message = event_info.value

Arguments

  • event str#

    Event name, same one typically passed into *.on(event).

  • predicate Callable (optional)#

    Receives the event data and resolves to truthy value when the waiting should resolve.

  • timeout float (optional)#

    Maximum time to wait for in milliseconds. Defaults to 30000 (30 seconds). Pass 0 to disable timeout. The default value can be changed by using the browser_context.set_default_timeout().

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

on("console")​

Added in: v1.57 worker.on("console")

Emitted when JavaScript within the worker calls one of console API methods, e.g. console.log or console.dir.

Usage

worker.on("console", handler)

Event data