I'm working with Node.js and Puppeteer for the first time and can't find a way to output values from page.evaluate
to the outer scope.
My algorithm:
ul
li
and click on itinnetHTML
to be set and add it's src
content to an array.How can I return data from page.evaluate()
?
const puppeteer = require('puppeteer');
const CREDENTIALS = require(`./env.js`).credentials;
const SELECTORS = require(`./env.js`).selectors;
const URLS = require(`./env.js`).urls;
async function run() {
try {
const urls = [];
const browser = await puppeteer.launch({headless: false});
const page = await browser.newPage();
await page.goto(URLS.login, {waitUntil: 'networkidle0'});
await page.type(SELECTORS.username, CREDENTIALS.username);
await page.type(SELECTORS.password, CREDENTIALS.password);
await page.click(SELECTORS.submit);
await page.waitForNavigation({waitUntil: 'networkidle0'});
await page.goto(URLS.course, {waitUntil: 'networkidle0'});
const nodes = await page.evaluate(selector => {
let elements = document.querySelector(selector).childNodes;
console.log('elements', elements);
return Promise.resolve(elements ? elements : null);
}, SELECTORS.list);
const links = await page.evaluate((urls, nodes, VIDEO) => {
return Array.from(nodes).forEach((node) => {
node.click();
return Promise.resolve(urls.push(document.querySelector(VIDEO).getAttribute('src')));
})
}, urls, nodes, SELECTORS.video);
const output = await links;
} catch (err) {
console.error('err:', err);
}
}
run();
The function page.evaluate()
can only return a serializable value, so it is not possible to return an element or NodeList
back from the page environment using this method.
You can use page.$$()
instead to obtain an ElementHandle
array:
const nodes = await page.$$(`${selector} > *`); // selector children
If the length
of the constant nodes
is 0
, then make sure you are waiting for the element specified by the selector to be added to the DOM with page.waitForSelector()
:
await page.waitForSelector(selector);
Use page.evaluateHandle()
An API is : here
let elementsHendles = await page.evaluateHandle(() => document.querySelectorAll('a'));
let elements = await elementsHendles.getProperties();
let elements_arr = Array.from(elements.values());
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