ExecutionContext.evaluate() method

Signature:

class ExecutionContext {
  evaluate<
    Params extends unknown[],
    Func extends EvaluateFunc<Params> = EvaluateFunc<Params>
  >(
    pageFunction: Func | string,
    ...args: Params
  ): Promise<Awaited<ReturnType<Func>>>;
}

Parameters

Parameter	Type	Description
pageFunction	Func | string	a function to be evaluated in the executionContext
args	Params	argument to pass to the page function

Returns:

Promise<Awaited<ReturnType<Func>>>

A promise that resolves to the return value of the given function.

Remarks

If the function passed to the executionContext.evaluate returns a Promise, then executionContext.evaluate would wait for the promise to resolve and return its value. If the function passed to the executionContext.evaluate returns a non-serializable value, then executionContext.evaluate resolves to undefined. DevTools Protocol also supports transferring some additional values that are not serializable by JSON: -0, NaN, Infinity, -Infinity, and bigint literals.

Example 1

const executionContext = await page.mainFrame().executionContext();
const result = await executionContext.evaluate(() => Promise.resolve(8 * 7))* ;
console.log(result); // prints "56"

Example 2

A string can also be passed in instead of a function.

console.log(await executionContext.evaluate('1 + 2')); // prints "3"

Example 3

JSHandle instances can be passed as arguments to the executionContext.* evaluate:

const oneHandle = await executionContext.evaluateHandle(() => 1);
const twoHandle = await executionContext.evaluateHandle(() => 2);
const result = await executionContext.evaluate(
   (a, b) => a + b, oneHandle, * twoHandle
);
await oneHandle.dispose();
await twoHandle.dispose();
console.log(result); // prints '3'.