How to use ShouldReturnTheElementHandle method of PuppeteerSharp.Tests.WaitTaskTests.FrameWaitForSelectorTests class

If you are using CSS selector as a locator then you haven't provided correct locator.

You can try following CSS Selector which should work.

Using Type attribute

await page.ClickAsync("button[type='submit']");

OR Using name attribute

 await page.ClickAsync("button[name='login-submit']");

OR using class attribute

await page.ClickAsync("button.inline-btn-2");

OR Using multiple attribute such as

await page.ClickAsync("button[type='submit'][name='login-submit']");

If you are using CSS selector as a locator then you haven't provided correct locator.

You can try following CSS Selector which should work.

Using Type attribute

await page.ClickAsync("button[type='submit']");

OR Using name attribute

 await page.ClickAsync("button[name='login-submit']");

OR using class attribute

await page.ClickAsync("button.inline-btn-2");

OR Using multiple attribute such as

await page.ClickAsync("button[type='submit'][name='login-submit']");

Change your Window_Loaded event method to async and do an await on the Init method, Event Handler methods are an exception. using async void instead of async Task is ok in this scenario. - Reference (Should I avoid 'async void' event handlers?):

private async void Window_Loaded(object sender, RoutedEventArgs e) 
{  
   await Handler.Init(Handler);
}

From the examples in the docs, it looks like you have to do this:

// select the tag first
var element = await _page.QuerySelectorAsync("h1 > strong > a");

// then get the attribute
var url = await element.EvaluateFunctionAsync<string>("e => e.getAttribute('href')");
// OR
var url = await _page.EvaluateFunctionAsync<string>("e => e.getAttribute('href')", element);
// OR
var url = await (await element.GetPropertyAsync("href")).JsonValueAsync<string>();

// OR all in one
var url = await _page.EvaluateExpressionAsync<string>($"document.querySelector({"'h1 > strong > a'"}).getAttribute('href')");

You gotta apply this to the value of a select option, of course. Probably 'value' instead of 'href' and the correct selector.

You can call EvaluateFunction passing that ElementHandle as an argument

var content = await Page.EvaluateFunctionAsync<string>("e => e.textContent", elementHandle);

If you have many scenarios like that, you can build an extension method to solve that for you ;)

This code will load www.kayak.com with no images:

using (var browser = await Puppeteer.LaunchAsync(new LaunchOptions { Headless = false }))
using (var page = await browser.NewPageAsync())
{
    await page.SetRequestInterceptionAsync(true);

    // disable images to download
    page.Request += (sender, e) =>
    {
        if (e.Request.ResourceType == ResourceType.Image)
            e.Request.AbortAsync();
        else
            e.Request.ContinueAsync();
    };
    await page.GoToAsync("https://www.kayak.com");
    Console.ReadLine();
}

You can use a headless browser to render the html and then take a snapshot.

Have a look at PuppeteerSHarp: https://github.com/kblok/puppeteer-sharp

To use XPath based and not CSS selection use page.XPathAsync(xpath-expression) e.g.

var tds = page.XPathAsync(".//td[contains(., 'ABC-DEF-GHI')]");
await tds[0].ClickAsync();

For local path, need to use file protocol like below:

await page.GoToAsync("file://" + Path.Combine(context.FunctionAppDirectory, "www", "index.html"));