Configure WebDriverIO with BrowserMobProxy

You can use the below code to do that. Make sure your browsermob proxy and selenium server is running. Then copy paste below code in a test.js file and put it in webdriverio installed folder. From cmd go to that folder and run node test.js . stuff.har should be generated where test.js is located.

var Proxy = require('browsermob-proxy').Proxy
    , webdriverio = require("./node_modules/webdriverio/")
    , fs = require('fs')
    , proxy = new Proxy()
;

proxy.cbHAR('search.yahoo.com', 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://search.yahoo.com")
        .setValue("#yschsp", "javascript")
        .submitForm("#sf")
        .end().then(cb);        

}

If you just want to capture the network traffic, then there is one more way to do it.

Webdriverio allows you to use Chrome Dev Tools Protocol.

Please read webdriverio blog

This is one of the examples on how to use chrome dev tools along with webdriverio, do let me know in case you need more help.

const { remote } = require('webdriverio')

    let browser;

    (async () => {
        browser = await remote({
            automationProtocol: 'devtools',
            capabilities: {
                browserName: 'chrome'
            }
        })

        await browser.url('https://webdriver.io')

        await browser.call(async () => {
            const puppeteerBrowser = browser.getPuppeteer()
            const page = (await puppeteerBrowser.pages())[0]
            await page.setRequestInterception(true)
            page.on('request', interceptedRequest => {
                if (interceptedRequest.url().endsWith('webdriverio.png')) {
                    return interceptedRequest.continue({
                        url: 'https://user-images.githubusercontent.com/10379601/29446482-04f7036a-841f-11e7-9872-91d1fc2ea683.png'
                    })
                }

                interceptedRequest.continue()
            })
        })

        // continue with WebDriver commands
        await browser.refresh()
        await browser.pause(2000)

        await browser.deleteSession()
    })().catch(async (e) => {
        console.error(e)
        await browser.deleteSession()
    })