JSHandle

JSHandle 表示页面内的 JavaScript 对象。可以使用 Page.evaluateHandle() 方法创建 JSHandle。

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

JSHandle windowHandle = page.evaluateHandle("() => window");
// ...

JSHandle 会阻止被引用的 JavaScript 对象被垃圾回收，除非通过 JSHandle.dispose() 显式释放该句柄。当 JSHandle 的源框架被导航或父上下文被销毁时，JSHandle 会自动释放。

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

JSHandle 实例可以作为参数用于 Page.evalOnSelector()、Page.evaluate() 和 Page.evaluateHandle() 方法。

🌐 JSHandle instances can be used as an argument in Page.evalOnSelector(), Page.evaluate() and Page.evaluateHandle() 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

JSHandle.asElement();

返回

• null | ElementHandle#

---

dispose

Added before v1.9 jsHandle.dispose

jsHandle.dispose 方法停止引用元素句柄。

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

用法

JSHandle.dispose();

返回

• void#

---

evaluate

Added before v1.9 jsHandle.evaluate

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 返回一个 Promise，那么 handle.evaluate 会等待该 promise 解决并返回其值。

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

用法

ElementHandle tweetHandle = page.querySelector(".tweet .retweets");
assertEquals("10 retweets", tweetHandle.evaluate("node => node.innerText"));

参数

• expression String#

  将在浏览器上下文中求值的 JavaScript 表达式。如果表达式求值为一个函数，该函数将被自动调用。

• arg EvaluationArgument (optional)#

  可选参数，传递给 expression。

返回

• Object#

---

evaluateHandle

Added before v1.9 jsHandle.evaluateHandle

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 唯一的区别是 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 的函数返回一个 Promise，那么 jsHandle.evaluateHandle 会等待该 promise 解决并返回其值。

🌐 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.

有关更多详细信息，请参见 Page.evaluateHandle()。

🌐 See Page.evaluateHandle() for more details.

用法

JSHandle.evaluateHandle(expression);
JSHandle.evaluateHandle(expression, arg);

参数

• expression String#

  将在浏览器上下文中求值的 JavaScript 表达式。如果表达式求值为一个函数，该函数将被自动调用。

• arg EvaluationArgument (optional)#

  可选参数，传递给 expression。

返回

• JSHandle#

---

getProperties

Added before v1.9 jsHandle.getProperties

该方法返回一个映射，其键为自身属性名，值为属性值对应的 JSHandle 实例。

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

用法

JSHandle handle = page.evaluateHandle("() => ({ window, document })");
Map<String, JSHandle> properties = handle.getProperties();
JSHandle windowHandle = properties.get("window");
JSHandle documentHandle = properties.get("document");
handle.dispose();

返回

• Map<String, JSHandle>#

---

getProperty

Added before v1.9 jsHandle.getProperty

从引用的对象中获取单个属性。

🌐 Fetches a single property from the referenced object.

用法

JSHandle.getProperty(propertyName);

参数

• propertyName String#

  获得的属性

返回

• JSHandle#

---

jsonValue

Added before v1.9 jsHandle.jsonValue

返回对象的 JSON 表示。如果对象有 toJSON 函数，不会被调用。

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

note

如果被引用的对象无法转换为字符串，该方法将返回一个空的 JSON 对象。如果对象具有循环引用，它将抛出错误。

🌐 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

JSHandle.jsonValue();

返回

• Object#