How can I programmatically disable Chromium’s 'Use browser default User-Agent' in Electron?

I am developing a custom Electron browser that dynamically modifies the User-Agent for specific domains. However, when I remove the Electron/* portion from the User-Agent for a demo gaming website, the site fails to load and throws JavaScript errors.

I intercept all outgoing requests in my Electron main.js using the following code:

JAVASCRIPTCopied
session.defaultSession.webRequest.onBeforeSendHeaders((details, callback) => {
    const originalUserAgent = details.requestHeaders['User-Agent'];
    const newUserAgent = getUserAgentForURL(originalUserAgent, details.url);

    console.log('========================');
    console.log('Intercepted Request:');
    console.log('URL:', details.url);
    console.log('Original User-Agent:', originalUserAgent);
    console.log('Modified User-Agent:', newUserAgent);
    console.log('========================');

    details.requestHeaders['User-Agent'] = newUserAgent;
    callback({ cancel: false, requestHeaders: details.requestHeaders });
});

My user-agent.js module modifies the User-Agent as shown below, removing Electron-specific components while retaining Chrome info:

JAVASCRIPTCopied
const { app } = require('electron');

const REMOVE_ELECTRON_COMPONENTS = [
  / Electron\/([^
\s]+)/g,  // Removes Electron
  ` ${app.name}/${app.getVersion()}`, // Removes app-specific info
];

function getUserAgentForURL(userAgent, url) {
  if (typeof userAgent !== 'string') {
    console.error(`Error: Expected userAgent to be a string, but got ${typeof userAgent}`);
    return userAgent || 'Mozilla/5.0';
  }

  let componentsToRemove = [...REMOVE_ELECTRON_COMPONENTS];

  // Remove Electron-specific components but keep Chrome
  componentsToRemove.forEach((x) => {
    if (userAgent) {
      userAgent = userAgent.replace(x, '');
    }
  });

  return userAgent;
}

module.exports = { getUserAgentForURL };

Debugging Output:

When trying to access the demo game website, the logs show:

BASHCopied
========================
Intercepted Request:
URL: https://[removed-domain]/game-assets/other_resources.json
Original User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) my-electron-app/1.0.0 Chrome/132.0.6834.159 Electron/34.0.2 Safari/537.36
Modified User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/132.0.6834.159 Safari/537.36
========================

However, the website does not load and throws these JavaScript errors:

BASHCopied
[96308:0201/114327.613:INFO:CONSOLE(5657)] "Uncaught TypeError: Cannot read properties of undefined (reading 'split')", 
source: https://[removed-domain]/build.js (5657)

[96308:0201/114327.616:INFO:CONSOLE(18588)] "Uncaught TypeError: Cannot read properties of null (reading 'length')", 
source: https://[removed-domain]/logo_info.js (18588)

When I do not modify the User-Agent, the website functions correctly. For example, a successful request logs the default User-Agent set by Electron:

BASHCopied
========================
Intercepted Request:
URL: https://[removed-domain]/gs2c/ge/v4/game
Method: POST
Headers: {
  "host": "[removed-domain]",
  "connection": "keep-alive",
  "content-length": "145",
  "accept": "*/*",
  "accept-encoding": "gzip, deflate, br, zstd",
  "accept-language": "en-US",
  "content-type": "application/x-www-form-urlencoded",
  "origin": "https://[removed-domain]",
  "referer": "https://[removed-domain]/gs2c/html5Game.do?extGame=1&symbol..",
  "sec-fetch-dest": "empty",
  "sec-fetch-mode": "cors",
  "sec-fetch-site": "same-origin",
  "user-agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) my-electron-app/1.0.0 Chrome/132.0.6834.159 Electron/34.0.2 Safari/537.36",
  "sec-ch-ua": "\"Not A(Brand\";v=\"8\", \"Chromium\";v=\"132\"",
  "sec-ch-ua-mobile": "?0",
  "sec-ch-ua-platform": "\"Windows\""
}
========================

UPDATE

I tested using the "User-Agent Switcher for Chrome" extension but the game still failed to load, indicating that Chrome ignored the changes. I later discovered the "Use browser default User-Agent" setting in DevTools → Network Conditions:

• Opened DevTools (F12) → Network Tab
• Clicked the Wi-Fi icon (bottom left)
• Found "Use browser default User-Agent" enabled by default

This setting causes conflicts: outgoing requests use the modified User-Agent, but the browser’s internal JavaScript runtime still uses the default, leading to errors. Unchecking this setting and manually entering the modified User-Agent allowed the game to load correctly.

My question is: How can I automatically disable the "Use browser default User-Agent" setting in Electron (via a command-line flag or API) so that the browser's internal behavior matches the modified User-Agent?