Intercepting requests with "JS" in "Chrome"?

Question

JavaScript

Good afternoon. Can anyone tell me how to intercept requests using JS in "Chrome"?
For example, so that for any request to some or all sites, the string "this is a response constructed by VPN extension" is returned to me.

Answer 1

If I understand correctly that you have your own extension, then:
Edit the manifest by adding "webRequest" to the permissions

"permissions": [
          "webRequest"
          // other permissions

Before sending a request, you can cancel it:

chrome.webRequest.onBeforeRequest.addListener(
        function(details) {
          if (details.url.indexOf("://white.listed.site")) console.log("this is a response constructed by VPN extension");
          return {cancel: details.url.indexOf("://www.evil.com/") != -1}; // если нужно отменить запрос
        },
        {urls: ["<all_urls>"]},
        ["blocking"]);

You can also hang onComplete

chrome.webRequest.onCompleted.addListener(function(details){
    console.log(`Catch ${details.method} response from ${details.url} ${details.fromCache ? ' [ from cache ]' : ''} `)
}