node.js - Exposed function querySelector not working in Puppeteer

Question

document.querySelectorAll('.summary').innerText;

This throws an error in the below snippet saying "document.querySelector is not a function" in my Puppeteer page's exposed fucntion docTest.

I want to pass a specific node to each method and get the result inside evaluate.

Same with document.getElemenetbyId.

const puppeteer = require('puppeteer');
//var querySelectorAll = require('query-selector');


let docTest = (document) => {
var summary = document.querySelectorAll(.summary).innerText;
console.log(summary);
return summary;
}

let scrape = async () => {

const browser = await puppeteer.launch({
    headless: false
});
const page = await browser.newPage();

await page.goto('http://localhost.com:80/static.html');
await page.waitFor(5000)
await page.exposeFunction('docTest', docTest);

var result = await page.evaluate(() => {
    var resultworking = document.querySelector("tr");
    console.log(resultworking);
    var summary  = docTest(document);
    console.log(resultworking);
    return summary;

});
console.log(result);

await page.waitFor(7000);
browser.close();
return {
    result
}
};

scrape().then((value) => {
console.log(value); // Success!
});

Answer 1

I just had the same question. The problem is that the page.evaluate() function callback has to be an async function and your function docTest() will return a Promise when called inside the page.evaluate(). To fix it, just add the async and await keywords to your code:

await page.exposeFunction('docTest', docTest);

var result = await page.evaluate(async () => {
    var summary = await docTest(document);
    console.log(summary);
    return summary;
});

Just remember that page.exposeFunction() will make your function return a Promise, then, you need to use async and await. This happens because your function will not be running inside your browser, but inside your nodejs application.

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