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JSHandle

JSHandle 表示页内 JavaScript 对象。JSHandles 可以使用 Page.EvaluateHandleAsync() 方法创建。

¥JSHandle represents an in-page JavaScript object. JSHandles can be created with the Page.EvaluateHandleAsync() method.

var windowHandle = await page.EvaluateHandleAsync("() => window");

JSHandle 会阻止引用的 JavaScript 对象被垃圾回收，除非该句柄通过 JsHandle.DisposeAsync() 公开。当导航其原始框架或父上下文被破坏时，JSHandles 会自动处置。

¥JSHandle prevents the referenced JavaScript object being garbage collected unless the handle is exposed with JsHandle.DisposeAsync(). JSHandles are auto-disposed when their origin frame gets navigated or the parent context gets destroyed.

JSHandle 实例可以用作 Page.EvalOnSelectorAsync()、Page.EvaluateAsync() 和 Page.EvaluateHandleAsync() 方法中的参数。

¥JSHandle instances can be used as an argument in Page.EvalOnSelectorAsync(), Page.EvaluateAsync() and Page.EvaluateHandleAsync() methods.

方法​

¥Methods

AsElement​

Added before v1.9 jsHandle.AsElement

如果对象句柄是 ElementHandle 的实例，则返回 null 或对象句柄本身。

¥Returns either null or the object handle itself, if the object handle is an instance of ElementHandle.

用法

¥Usage

JsHandle.AsElement();

返回

¥Returns

DisposeAsync​

Added before v1.9 jsHandle.DisposeAsync

jsHandle.dispose 方法停止引用元素句柄。

¥The jsHandle.dispose method stops referencing the element handle.

用法

¥Usage

await JsHandle.DisposeAsync();

返回

¥Returns

EvaluateAsync​

Added before v1.9 jsHandle.EvaluateAsync

返回 expression 的返回值。

¥Returns the return value of expression.

此方法将此句柄作为第一个参数传递给 expression。

¥This method passes this handle as the first argument to expression.

如果 expression 返回 Promise，那么 handle.evaluate 将等待 Promise 解析并返回其值。

¥If expression returns a Promise, then handle.evaluate would wait for the promise to resolve and return its value.

用法

¥Usage

var tweetHandle = await page.QuerySelectorAsync(".tweet .retweets");
Assert.AreEqual("10 retweets", await tweetHandle.EvaluateAsync("node => node.innerText"));

参数

¥Arguments

要在浏览器上下文中执行的 JavaScript 表达式。如果表达式的计算结果为函数，则会自动调用该函数。

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

传递给 expression 的可选参数。

¥Optional argument to pass to expression.

返回

¥Returns

  • [object]#

EvaluateHandleAsync​

Added before v1.9 jsHandle.EvaluateHandleAsync

将 expression 的返回值作为 JSHandle 返回。

¥Returns the return value of expression as a JSHandle.

此方法将此句柄作为第一个参数传递给 expression。

¥This method passes this handle as the first argument to expression.

jsHandle.evaluate 和 jsHandle.evaluateHandle 之间的唯一区别是 jsHandle.evaluateHandle 返回 JSHandle。

¥The only difference between jsHandle.evaluate and jsHandle.evaluateHandle is that jsHandle.evaluateHandle returns JSHandle.

如果传递给 jsHandle.evaluateHandle 的函数返回 Promise，那么 jsHandle.evaluateHandle 将等待 Promise 解析并返回其值。

¥If the function passed to the jsHandle.evaluateHandle returns a Promise, then jsHandle.evaluateHandle would wait for the promise to resolve and return its value.

详细信息请参见 Page.EvaluateHandleAsync()。

¥See Page.EvaluateHandleAsync() for more details.

用法

¥Usage

await JsHandle.EvaluateHandleAsync(expression, arg);

参数

¥Arguments

要在浏览器上下文中执行的 JavaScript 表达式。如果表达式的计算结果为函数，则会自动调用该函数。

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

传递给 expression 的可选参数。

¥Optional argument to pass to expression.

返回

¥Returns

GetPropertiesAsync​

Added before v1.9 jsHandle.GetPropertiesAsync

该方法返回一个映射，其中自己的属性名称作为键，JSHandle 实例作为属性值。

¥The method returns a map with own property names as keys and JSHandle instances for the property values.

用法

¥Usage

var handle = await page.EvaluateHandleAsync("() => ({ window, document }");
var properties = await handle.GetPropertiesAsync();
var windowHandle = properties["window"];
var documentHandle = properties["document"];
await handle.DisposeAsync();

返回

¥Returns

GetPropertyAsync​

Added before v1.9 jsHandle.GetPropertyAsync

从引用的对象中获取单个属性。

¥Fetches a single property from the referenced object.

用法

¥Usage

await JsHandle.GetPropertyAsync(propertyName);

参数

¥Arguments

获得的属性

¥property to get

返回

¥Returns

JsonValueAsync​

Added before v1.9 jsHandle.JsonValueAsync

返回对象的 JSON 表示形式。如果对象有 toJSON 函数，则不会调用它。

¥Returns a JSON representation of the object. If the object has a toJSON function, it will not be called.

注意

如果引用的对象不可字符串化，该方法将返回一个空的 JSON 对象。如果对象有循环引用，则会抛出错误。

¥The method will return an empty JSON object if the referenced object is not stringifiable. It will throw an error if the object has circular references.

用法

¥Usage

await JsHandle.JsonValueAsync();

返回

¥Returns

  • [object]#