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执行 JavaScript

Playwright 脚本在您的 Playwright 环境中运行。您的页面脚本在浏览器页面环境中运行。这些环境不相交，它们在不同进程中的不同虚拟机中运行，甚至可能在不同的计算机上运行。

page.evaluate(expression, **kwargs) API 可以在网页上下文中运行 JavaScript 函数，并将结果带回 Playwright 环境。浏览器全局变量（如 window 和 document）可用于 evaluate。

href = page.evaluate('() => document.location.href')

如果结果是 Promise 或函数是异步的，evaluate 将自动等待直到它被解析：

status = page.evaluate("""async () => {
  response = await fetch(location.href)
  return response.status
}""")

Evaluation Argument​

Playwright 执行方法（如 page.evaluate(expression, **kwargs)）接受一个可选参数。此参数可以是 Serializable 值和 JSHandle 或 ElementHandle 实例的混合。句柄会自动转换为它们表示的值。

# A primitive value.
page.evaluate('num => num', 42)

# An array.
page.evaluate('array => array.length', [1, 2, 3])

# An object.
page.evaluate('object => object.foo', { 'foo': 'bar' })

# A single handle.
button = page.evaluate('window.button')
page.evaluate('button => button.textContent', button)

# Alternative notation using elementHandle.evaluate.
button.evaluate('(button, from) => button.textContent.substring(from)', 5)

# Object with multiple handles.
button1 = page.evaluate('window.button1')
button2 = page.evaluate('.button2')
page.evaluate("""o => o.button1.textContent + o.button2.textContent""",
    { 'button1': button1, 'button2': button2 })

# Object destructuring works. Note that property names must match
# between the destructured object and the argument.
# Also note the required parenthesis.
page.evaluate("""
    ({ button1, button2 }) => button1.textContent + button2.textContent""",
    { 'button1': button1, 'button2': button2 })

# Array works as well. Arbitrary names can be used for destructuring.
# Note the required parenthesis.
page.evaluate("""
    ([b1, b2]) => b1.textContent + b2.textContent""",
    [button1, button2])

# Any non-cyclic mix of serializables and handles works.
page.evaluate("""
    x => x.button1.textContent + x.list[0].textContent + String(x.foo)""",
    { 'button1': button1, 'list': [button2], 'foo': None })

正确：

data = { 'text': 'some data', 'value': 1 }
# Pass |data| as a parameter.
result = page.evaluate("""data => {
  window.myApp.use(data)
}""", data)

错误：

data = { 'text': 'some data', 'value': 1 }
result = page.evaluate("""() => {
  # There is no |data| in the web page.
  window.myApp.use(data)
}""")