class: Worker

Worker 类表示一个 WebWorker。在页面对象上 workercreated 和 workerdestroyed 事件被触发，以标识 worker 的生命周期。

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());

worker.evaluate(pageFunction, ...args)

• pageFunction <function|string> Function to be evaluated in the worker context
• ...args <...Serializable|JSHandle> Arguments to pass to pageFunction
• returns: <Promise<Serializable>> Promise which resolves to the return value of pageFunction

如果传递给 worker.evaluate 的函数返回一个 Promise，那么 worker.evaluate 将等待解析并返回它的值。

如果传递给 worker.evaluate 的函数返回一个 非[序列化]的值，那么 worker.evaluate 解析为 undefined。

(await worker.executionContext()).evaluate(pageFunction, ...args) 的快捷链接。

worker.evaluateHandle(pageFunction, ...args)

• pageFunction <function|string> Function to be evaluated in the page context
• ...args <...Serializable|JSHandle> Arguments to pass to pageFunction
• returns: <Promise<JSHandle>> Promise which resolves to the return value of pageFunction as in-page object (JSHandle)

worker.evaluate 和 worker.evaluateHandle 之间的唯一区别是 worker.evaluateHandle 返回页内对象（JSHandle）。

如果传递给 worker.evaluateHandle 的函数返回一个 Promise，那么 worker.evaluateHandle 将等待解析并返回它的值。

(await worker.executionContext()).evaluateHandle(pageFunction, ...args) 的快捷链接。

worker.executionContext()

• returns: <Promise<ExecutionContext>>

worker.url()

• returns: <string>