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JSHandle

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

const windowHandle = await page.evaluateHandle(() => window);
// ...

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 instances can be used as an argument in page.$eval(), page.evaluate() and page.evaluateHandle() methods.

方法 (Methods)​

asElement​

Added before v1.9 jsHandle.asElement

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

使用方式

jsHandle.asElement();

傳回值

dispose​

Added before v1.9 jsHandle.dispose

The jsHandle.dispose method stops referencing the element handle.

使用方式

await jsHandle.dispose();

傳回值

evaluate​

Added before v1.9 jsHandle.evaluate

Returns the return value of pageFunction.

This method passes this handle as the first argument to pageFunction.

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

使用方式

const tweetHandle = await page.$('.tweet .retweets');
expect(await tweetHandle.evaluate(node => node.innerText)).toBe('10 retweets');

參數

傳回值

evaluateHandle​

Added before v1.9 jsHandle.evaluateHandle

Returns the return value of pageFunction as a JSHandle.

This method passes this handle as the first argument to pageFunction.

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

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.

See page.evaluateHandle() for more details.

使用方式

await jsHandle.evaluateHandle(pageFunction);
await jsHandle.evaluateHandle(pageFunction, arg);

參數

傳回值

getProperties​

Added before v1.9 jsHandle.getProperties

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

使用方式

const handle = await page.evaluateHandle(() => ({ window, document }));
const properties = await handle.getProperties();
const windowHandle = properties.get('window');
const documentHandle = properties.get('document');
await handle.dispose();

傳回值

getProperty​

Added before v1.9 jsHandle.getProperty

Fetches a single property from the referenced object.

使用方式

await jsHandle.getProperty(propertyName);

參數

  • propertyName string#

    property to get

傳回值

jsonValue​

Added before v1.9 jsHandle.jsonValue

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

note

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.

使用方式

await jsHandle.jsonValue();

傳回值