Add-ons

webRequest.StreamFilter.onstart

An event handler that will be called when when the stream is opened and is about to begin delivering data. From this point on, the extension may use filter functions like write(), disconnect(), or close().

Browser compatibility

ChromeEdgeFirefoxFirefox for AndroidOpera
Basic support No No5757 No

Examples

This example will replace the page content with "replacement text":

function listener(details) {
  let filter = browser.webRequest.filterResponseData(details.requestId);

  filter.onstart = event => {
    console.log("started");
    let encoder = new TextEncoder();
    filter.write(encoder.encode("replacement content"));
    filter.close();
  }
}

browser.webRequest.onBeforeRequest.addListener(
  listener,
  {urls: ["https://example.org/"], types: ["main_frame"]},
  ["blocking"]
);

Document Tags and Contributors

 Contributors to this page: wbamberg
 Last updated by: wbamberg,