Capture network traffic using BrowserMob, selenium server and below code. For more details , refer my this answer. Then parse stuff.har , to get desired result. Har file is in json format.
var Proxy = require('browsermob-proxy').Proxy
    , webdriverio = require("./node_modules/webdriverio/")
    , fs = require('fs')
    , proxy = new Proxy()
;
proxy.cbHAR('webdriver.io', doSeleniumStuff, function(err, data) {
        if (err) {
            console.error('ERR: ' + err);
        } else {
            fs.writeFileSync('stuff.har', data, 'utf8');
        }
});
function doSeleniumStuff(proxy, cb) {
    var browser = webdriverio.remote({
        host: 'localhost'
        , port: 4444
        , desiredCapabilities: { browserName: 'firefox', seleniumProtocol: 'WebDriver', proxy: { httpProxy: proxy } }
    });
    browser
        .init()
        .url("http://webdriver.io")
        //.setValue("#yschsp", "javascript")
        //.submitForm("#sf")
        .end().then(cb);        
}