Scrolling down to the bottom of the page can be accomplished in 2 ways:
- use scrollIntoView (to scroll to the part of the page that can create more content at the bottom) and selectors (i.e.,
document.querySelectorAll('.class_name').length to check whether more content has been generated)
- use scrollBy (to incrementally scroll down the page) and either setTimeout or setInterval (to incrementally check whether we are at the bottom of the page)
Here is an implementation using scrollIntoView and selector (assuming .class_name is the selector that we scroll into for more content) in plain JavaScript that we can run in the browser:
Method 1: use scrollIntoView and selectors
const delay = 3000;
const wait = (ms) => new Promise(res => setTimeout(res, ms));
const count = async () => document.querySelectorAll('.class_name').length;
const scrollDown = async () => {
document.querySelector('.class_name:last-child')
.scrollIntoView({ behavior: 'smooth', block: 'end', inline: 'end' });
}
let preCount = 0;
let postCount = 0;
do {
preCount = await count();
await scrollDown();
await wait(delay);
postCount = await count();
} while (postCount > preCount);
await wait(delay);
In this method, we are comparing the # of .class_name selectors before scrolling (preCount) vs after scrolling (postCount) to check whether we are at bottom of page:
if (postCount > precount) {
// NOT bottom of page
} else {
// bottom of page
}
And here are 2 possible implementations using either setTimeout or setInterval with scrollBy in plain JavaScript that we can run in the browser console:
Method 2a: use setTimeout with scrollBy
const distance = 100;
const delay = 100;
while (document.scrollingElement.scrollTop + window.innerHeight < document.scrollingElement.scrollHeight) {
document.scrollingElement.scrollBy(0, distance);
await new Promise(resolve => { setTimeout(resolve, delay); });
}
Method 2b: use setInterval with scrollBy
const distance = 100;
const delay = 100;
const timer = setInterval(() => {
document.scrollingElement.scrollBy(0, distance);
if (document.scrollingElement.scrollTop + window.innerHeight >= document.scrollingElement.scrollHeight) {
clearInterval(timer);
}
}, delay);
In this method, we are comparing document.scrollingElement.scrollTop + window.innerHeight with document.scrollingElement.scrollHeight to check whether we are at the bottom of the page:
if (document.scrollingElement.scrollTop + window.innerHeight < document.scrollingElement.scrollHeight) {
// NOT bottom of page
} else {
// bottom of page
}
If either of the JavaScript code above scrolls the page all the way down to the bottom, then we know it is working and we can automate this using Puppeteer.
Here are the sample Puppeteer Node.js scripts that will scroll down to the bottom of the page and wait a few seconds before closing the browser.
Puppeteer Method 1: use scrollIntoView with selector (.class_name)
const puppeteer = require('puppeteer');
(async () => {
const browser = await puppeteer.launch({
headless: false,
defaultViewport: null,
args: ['--window-size=800,600']
});
const page = await browser.newPage();
await page.goto('https://example.com');
const delay = 3000;
let preCount = 0;
let postCount = 0;
do {
preCount = await getCount(page);
await scrollDown(page);
await page.waitFor(delay);
postCount = await getCount(page);
} while (postCount > preCount);
await page.waitFor(delay);
await browser.close();
})();
async function getCount(page) {
return await page.$$eval('.class_name', a => a.length);
}
async function scrollDown(page) {
await page.$eval('.class_name:last-child', e => {
e.scrollIntoView({ behavior: 'smooth', block: 'end', inline: 'end' });
});
}
Puppeteer Method 2a: use setTimeout with scrollBy
const puppeteer = require('puppeteer');
(async () => {
const browser = await puppeteer.launch({
headless: false,
defaultViewport: null,
args: ['--window-size=800,600']
});
const page = await browser.newPage();
await page.goto('https://example.com');
await scrollToBottom(page);
await page.waitFor(3000);
await browser.close();
})();
async function scrollToBottom(page) {
const distance = 100; // should be less than or equal to window.innerHeight
const delay = 100;
while (await page.evaluate(() => document.scrollingElement.scrollTop + window.innerHeight < document.scrollingElement.scrollHeight)) {
await page.evaluate((y) => { document.scrollingElement.scrollBy(0, y); }, distance);
await page.waitFor(delay);
}
}
Puppeteer Method 2b: use setInterval with scrollBy
const puppeteer = require('puppeteer');
(async () => {
const browser = await puppeteer.launch({
headless: false,
defaultViewport: null,
args: ['--window-size=800,600']
});
const page = await browser.newPage();
await page.goto('https://example.com');
await page.evaluate(scrollToBottom);
await page.waitFor(3000);
await browser.close();
})();
async function scrollToBottom() {
await new Promise(resolve => {
const distance = 100; // should be less than or equal to window.innerHeight
const delay = 100;
const timer = setInterval(() => {
document.scrollingElement.scrollBy(0, distance);
if (document.scrollingElement.scrollTop + window.innerHeight >= document.scrollingElement.scrollHeight) {
clearInterval(timer);
resolve();
}
}, delay);
});
}
