Page.evaluate() method

Signature:

evaluate<ReturnType extends any>(pageFunction: Function | string, ...args: unknown[]): Promise<ReturnType>;

Parameters

Parameter	Type	Description
pageFunction	Function \| string	a function that is run within the page
args	unknown[]	arguments to be passed to the pageFunction

Returns:

Promise<ReturnType>

the return value of pageFunction.

Evaluates a function in the page's context and returns the result.

If the function passed to page.evaluteHandle returns a Promise, the function will wait for the promise to resolve and return its value.

const result = await frame.evaluate(() => {
  return Promise.resolve(8 * 7);
});
console.log(result); // prints "56"

You can pass a string instead of a function (although functions are recommended as they are easier to debug and use with TypeScript):

const aHandle = await page.evaluate('1 + 2');

ElementHandle instances (including JSHandles) can be passed as arguments to the pageFunction:

const bodyHandle = await page.$('body');
const html = await page.evaluate(body => body.innerHTML, bodyHandle);
await bodyHandle.dispose();