Long story short
I work with puppeteer a lot and wanted this knowlegde to be in my bag. One way to select a shadow Element is by accessing the parent DOM Node's shadowRoot property. The answer is based on this article.
Accessing Shadow Root property
For your html example this does the trick:
const button = document.querySelector('.shadow').shadowRoot.querySelector('#hoge')
waiting
Waiting though is a little more complicated but can be acquired using page.waitForFunction().
Working Sandbox
I wrote this full working sandbox example on how to wait for a certain shadowRoot element.
- index.html (located in same directory as app.js)
<html>
<head>
<script>
// attach shadowRoot after 6 seconds for emulating waiting..
setTimeout(() => {
const btn = document.getElementById('hoge')
const container = document.getElementsByClassName('shadow')[0]
const shadowRoot = container.attachShadow({
mode: 'open'
})
shadowRoot.innerHTML = `<button id="hoge" onClick="doStuff()">hoge2</button>`
console.log('attached!.')
}, 6000)
function doStuff() {
alert('shadow button clicked!')
}
</script>
</head>
<body>
<button id="hoge">Hoge</button>
<div class="shadow">
</div>
</body>
</html>
- app.js (located in same directory as index.html)
var express = require('express')
var { join } = require('path')
var puppeteer = require('puppeteer')
//utility..
const wait = (seconds) => {
console.log('waiting', seconds, 'seconds')
return new Promise((res, rej) => {
setTimeout(res, seconds * 1000)
})
}
const runPuppeteer = async() => {
const browser = await puppeteer.launch({
defaultViewport: null,
headless: false
})
const page = await browser.newPage()
await page.goto('http://127.0.0.1:5000')
await wait(3)
console.log('page opened..')
// only execute this function within a page context!.
// for example in page.evaluate() OR page.waitForFunction etc.
// don't forget to pass the selector args to the page context function!
const selectShadowElement = (containerSelector, elementSelector) => {
try {
// get the container
const container = document.querySelector(containerSelector)
// Here's the important part, select the shadow by the parentnode of the
// actual shadow root and search within the shadowroot which is like another DOM!,
return container.shadowRoot.querySelector(elementSelector)
} catch (err) {
return null
}
}
console.log('waiting for shadow elemetn now.')
const containerSelector = '.shadow'
const elementSelector = '#hoge'
const result = await page.waitForFunction(selectShadowElement, { timeout: 15 * 1000 }, containerSelector, elementSelector)
if (!result) {
console.error('Shadow element not found..')
return
}
// since waiting succeeded we can get the elemtn now.
const element = await page.evaluateHandle(selectShadowElement, containerSelector, elementSelector)
try {
// click the element.
await element.click()
console.log('clicked')
} catch (err) {
console.log('failed to click..')
}
await wait(10)
}
var app = express()
app.get('/', (req, res) => {
res.sendFile(join(__dirname, 'index.html'))
})
app.listen(5000, '127.0.0.1', () => {
console.log('listening!')
runPuppeteer()
})
Start example
$ npm i express puppeteer
$ node app.js
Make sure to use headless:false option to see what's happening.
The application does this:
- start a small
express server only serving index.html on /
- open
puppeteer after server has started and wait for the shadow root element to appear.
- Once it appeared, it gets clicked and an
alert() is shown. => success!
Browser Support
Tested with chrome.
Cheers ' ^^
