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Get a CF Worker to remove selected elements from a pages HTML
// set the site we are modifying
const site = 'www.example.com';
// do this on a fetch
addEventListener('fetch', event => {
const request = event.request
const url = new URL(request.url)
event.respondWith(handleRequest(request))
});
async function handleRequest(request) {
// store the URL
const url = new URL(request.url);
// disallow crawlers (write a robots.txt file)
if(url.pathname === "/robots.txt") {
return new Response('User-agent: *\nDisallow: /', {status: 200});
}
// when overrideHost is used in a WPT script, WPT sets x-host to original host i.e. site we want to proxy
// store the value of x-host
const xhost = request.headers.get('x-host');
// If this header is missing, abort
if(!xhost) {
return new Response('x-host header missing', {status: 403});
}
// set our hostname to that listed in the xhost header
url.hostname = xhost;
// look for header that allows us to bypass the transform entirely
const bypassTransform = request.headers.get('x-bypass-transform');
// get the accept header to allow us to examine the type of request it is
const acceptHeader = request.headers.get('accept');
if(xhost === site && (!bypassTransform || (bypassTransform && bypassTransform.indexOf('true') === -1))){
if(acceptHeader && acceptHeader.indexOf('text/html') >= 0){
// store this particular request for modification
let oldResponse = await fetch(url.toString(), request)
// create a new response
let newResponse = new HTMLRewriter()
// remove a specific script
.on("script[src*='name-of-our-script.js']", new removeElement())
// remove the third meta tag in the head
.on("head > meta:nth-of-type(3)", new removeElement())
// remove all div elements that start with 'prefix'
.on("div[class^='prefix']", new removeElement())
// remove all link elements that start with '/assets/' and end with '.css'
.on("link[href^='/assets/'][href$='.css']", new removeElement())
.transform(oldResponse)
// return the modified page along with custom headers
return newResponse
}
}
// otherwise just proxy the request unmodified
return fetch(url.toString(), request)
}
class removeElement {
element(element) {
element.remove();
}
}
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