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 ;)

We cannot convert the whole code for you but here are some pointers. You need to take one chunk of problem at a time.

Break the while loop

Let us look into the JS code,

let count = 0;
while (await page.$('#search-content button.btn-icon') !== null && count != 1) {}

It's creating a while look, which stops if count is 1.

Now your C# Code,

while (await page.QuerySelectorAsync("#search-content button.btn-icon") != null)

It's not checking for count, this will end up in infinite while loop.

You should count the number,

int count = 0;
while (await page.QuerySelectorAsync("#search-content button.btn-icon") != null && count != 1){
 // other code
 count++;
}

This way it will stop after it finds one result.

Learn more about Promise.all etc.

Your rest of the question is about Promise.all and few other stuff. Here are some useful links,

• Promise.all()
• API Documentation for Puppeteer Sharp
• API Documentation for Puppeteer

Although there are still many improvements going on, Puppeteer-Sharp is thread-safe. To improve loading performance, there are a few approaches you can take.

Launch one browser and then connect to it

You can launch one (real) browser and then use the ConnectAsync method to connect to it.

await new BrowserFetcher().DownloadAsync(BrowserFetcher.DefaultRevision);
var browser = await Puppeteer.LaunchAsync(new LaunchOptions
{
    Headless = false,
});

var theBrowser1 = await Puppeteer.ConnectAsync(new ConnectOptions { BrowserWSEndpoint = browser.WebSocketEndpoint });
var theBrowser2 = await Puppeteer.ConnectAsync(new ConnectOptions { BrowserWSEndpoint = browser.WebSocketEndpoint });
var page1 = await theBrowser1.NewPageAsync();
var page2 = await theBrowser2.NewPageAsync();

await Task.WhenAll(
    page1.GoToAsync("https://www.stackoverflow.com"),
    page2.GoToAsync("https://serverfault.com/")
);

I know that code is not running in parallel, but you'll get the idea about reusing the same browser.

Create new pages on the same browser

If you are using TPL, you shouldn't have any issues creating new pages from different threads using the same browser.

await new BrowserFetcher().DownloadAsync(BrowserFetcher.DefaultRevision);
var browser = await Puppeteer.LaunchAsync(new LaunchOptions
{
    Headless = false,
});

var urls = new string[]
{
    "https://www.stackoverflow.com",
    "https://www.stackoverflow.com",
    "https://www.stackoverflow.com",
    "https://www.stackoverflow.com",
    "https://www.stackoverflow.com",
    "https://www.stackoverflow.com",
    "https://www.stackoverflow.com",
    "https://www.stackoverflow.com",
    "https://www.stackoverflow.com",
    "https://www.stackoverflow.com",
    "https://www.stackoverflow.com"
};

await Task.WhenAll(
    urls.Select(url => Task.Factory.StartNew(async () =>
    {
        var page = await browser.NewPageAsync();
        return page.GoToAsync(url);
    })));

Again, this example is just to give you an idea of how this could be accomplished.

Pages queue

There is one user who created a queue of X pages (for x from 0 to X => NewPage) and then he would grab pages from that queue. You can see the example here.

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();
}

"TimeoutError: Timed out after 30000 ms while trying to connect to the browser! Only Chrome at revision r1056772 is guaranteed to work." might be an explanation, as of 12/2022. Tried on Chrome Portable and got this error, very similar to yours.

I found a solution: If the pages will be created in the same scope as their browser instance, then the pages will be created as expected, otherwise Task.Run() will be stuck due to NewPageAsync() method.

Bad behaviour:

Task[] Tasks = new Task[1];
Browser browser = await Puppeteer.LaunchAsync
(
    new LaunchOptions
    {
        Headless = true,
        ExecutablePath = "Chromium\\chrome.exe"
    }
);
for (int i = 0; i < Tasks.Length; i++)
{
    int ThreadNumber = i;
    Tasks[i] = Task.Run(async () =>
    {
       Page page = await browser.NewPageAsync(); //stucks
    });
}

Task.WaitAll(Tasks);

As expected:

Task[] Tasks = new Task[1];
for (int i = 0; i < Tasks.Length; i++)
{
    int ThreadNumber = i;
    Tasks[i] = Task.Run(async () =>
    {
       Browser browser = await Puppeteer.LaunchAsync
       (
           new LaunchOptions
           {
                Headless = true,
               ExecutablePath = "Chromium\\chrome.exe"
           }
       );
       Page page = await browser.NewPageAsync(); //creates as expected
    });
}

Task.WaitAll(Tasks);

Anyway this is not the best solution because I have to create browsers for async tasks rather than using one browser for all async tasks. Hope someone can explain that. Thanks everyone for helping!

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.

I found this is the most scalable way to implement this is by using a background process. This is one real-life example:

1. A WebClient request a PDF sending a signalR message.
2. The SignalR hub creates some kind of an ID, put the request in an Azure Queue, and adds the SignalR client to a SignalR group with that ID.
3. A console app would read that queue, process the HTML, and sends back the result to the server using a SignalR message.
4. The WebServer will get the message, and broadcast that message to all the clients in that group.

It might sound quite complicated, but it's not that much. You can make it simpler.

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);
}