class: 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 disposed. 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.

• jsHandle.asElement()
• jsHandle.dispose()
• jsHandle.evaluate(pageFunction[, arg])
• jsHandle.evaluateHandle(pageFunction[, arg])
• jsHandle.getProperties()
• jsHandle.getProperty(propertyName)
• jsHandle.jsonValue()

jsHandle.asElement()

• returns: <?ElementHandle>

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

jsHandle.dispose()

• returns: <Promise> Promise which resolves when the object handle is successfully disposed.

The jsHandle.dispose method stops referencing the element handle.

jsHandle.evaluate(pageFunction[, arg])

• pageFunction <function(Object)> Function to be evaluated in browser context
• arg <Serializable|JSHandle> Optional argument to pass to pageFunction
• returns: <Promise<Serializable>> Promise which resolves to 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.

Examples:

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

jsHandle.evaluateHandle(pageFunction[, arg])

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

jsHandle.getProperties()

• returns: <Promise<Map<string, JSHandle>>>

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

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();

jsHandle.getProperty(propertyName)

• propertyName <string> property to get
• returns: <Promise<JSHandle>>

Fetches a single property from the referenced object.

jsHandle.jsonValue()

• returns: <Promise<Object>>

Returns a JSON representation of the object. If the object has a toJSON_behavior) 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.