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Version: 1.17

Evaluating JavaScript

Playwright scripts run in your Playwright environment. Your page scripts run in the browser page environment. Those environments don't intersect, they are running in different virtual machines in different processes and even potentially on different computers.

The page.evaluate(pageFunction[, arg]) API can run a JavaScript function in the context of the web page and bring results back to the Playwright environment. Browser globals like window and document can be used in evaluate.

const href = await page.evaluate(() => document.location.href);

If the result is a Promise or if the function is asynchronous evaluate will automatically wait until it's resolved:

const status = await page.evaluate(async () => {
const response = await fetch(location.href);
return response.status;
});

Evaluation Argument

Playwright evaluation methods like page.evaluate(pageFunction[, arg]) take a single optional argument. This argument can be a mix of Serializable values and JSHandle or ElementHandle instances. Handles are automatically converted to the value they represent.

// A primitive value.
await page.evaluate(num => num, 42);

// An array.
await page.evaluate(array => array.length, [1, 2, 3]);

// An object.
await page.evaluate(object => object.foo, { foo: 'bar' });

// A single handle.
const button = await page.evaluate('window.button');
await page.evaluate(button => button.textContent, button);

// Alternative notation using elementHandle.evaluate.
await button.evaluate((button, from) => button.textContent.substring(from), 5);

// Object with multiple handles.
const button1 = await page.evaluate('window.button1');
const button2 = await page.evaluate('window.button2');
await page.evaluate(
o => o.button1.textContent + o.button2.textContent,
{ button1, button2 });

// Object destructuring works. Note that property names must match
// between the destructured object and the argument.
// Also note the required parenthesis.
await page.evaluate(
({ button1, button2 }) => button1.textContent + button2.textContent,
{ button1, button2 });

// Array works as well. Arbitrary names can be used for destructuring.
// Note the required parenthesis.
await page.evaluate(
([b1, b2]) => b1.textContent + b2.textContent,
[button1, button2]);

// Any non-cyclic mix of serializables and handles works.
await page.evaluate(
x => x.button1.textContent + x.list[0].textContent + String(x.foo),
{ button1, list: [button2], foo: null });

Right:

const data = { text: 'some data', value: 1 };
// Pass |data| as a parameter.
const result = await page.evaluate(data => {
window.myApp.use(data);
}, data);

Wrong:

const data = { text: 'some data', value: 1 };
const result = await page.evaluate(() => {
// There is no |data| in the web page.
window.myApp.use(data);
});