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.

Methods​

asElement​

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

Usage

jsHandle.asElement();

Returns

• null | ElementHandle

dispose​

The jsHandle.dispose method stops referencing the element handle.

Usage

await jsHandle.dispose();

Returns

• Promise<void>

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.

Usage

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

Arguments

• pageFunction function | string

  Function to be evaluated in the page context.

• arg EvaluationArgument (optional)

  Optional argument to pass to pageFunction.

Returns

• Promise<Serializable>

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.

Usage

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

Arguments

• pageFunction function | string

  Function to be evaluated in the page context.

• arg EvaluationArgument (optional)

  Optional argument to pass to pageFunction.

Returns

• Promise<JSHandle>

getProperties​

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

Usage

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();

Returns

• Promise<Map<string, JSHandle>>

getProperty​

Fetches a single property from the referenced object.

Usage

await jsHandle.getProperty(propertyName);

Arguments

• propertyName string

  property to get

Returns

• Promise<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.

Usage

await jsHandle.jsonValue();

Returns

• Promise<Serializable>