Simple .NET WebView2 DevTools helper to make it possible to invoke async Javascript code (see https://github.com/MicrosoftEdge/WebView2Feedback/issues/416#issuecomment-1073533384)

Main.cs

public static async Task Main()
{
	/*
	*	Use this codesnippet inside your WinForm/WPF WebView2 application
	*/
	var wv2 = new WebView2();
	await wv2.EnsureCoreWebView2Async();
	var devTools = new WebView2DevTools(wv2.CoreWebView2);
	
	// Some result vom Javascript
	var result = int.Parse(await devTools.EvaluateAsync("(function() { return Promise.resolve(42); })()"));
	
	// A function without result but some execution time (2 seconds)
	await devTools.EvaluateAsync("Promise(resolve => setTimeout(resolve, 2000))");
}

WebView2DevTools.cs

/*
* @copyright Copyright (c) 2022 Robin Windey <ro.windey@gmail.com>
* 
* @license GNU AGPL version 3 or any later version
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License as
* published by the Free Software Foundation, either version 3 of the
* License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program.  If not, see <http://www.gnu.org/licenses/>.
* ---------------------------------------------------------------------------
* This helper makes it possible to invoke and await async Javascript code via
* WebView2 DevTools interface to overcome the issue mentioned at
* https://github.com/MicrosoftEdge/WebView2Feedback/issues/416#issuecomment-1073533384
* 
*	To use this class make sure you have the following NuGet packages installed in your project:
*		- https://www.nuget.org/packages/Newtonsoft.Json/
*		- https://www.nuget.org/packages/Microsoft.Web.WebView2/
*
*   Class is highly inspired by
*       - https://docs.microsoft.com/en-us/microsoft-edge/webview2/how-to/chromium-devtools-protocol
*       - https://github.com/ChromiumDotNet/WebView2.DevTools.Dom
*       - https://github.com/hardkoded/puppeteer-sharp
*/
using System;
using System.Threading.Tasks;
using Microsoft.Web.WebView2.Core;
using Newtonsoft.Json;
using Newtonsoft.Json.Serialization;

namespace MyNamespace
{
    /// <summary>
    /// Implements the <see cref="EvaluateAsync(string)"/> function via chrome
    /// devtools protocol to ensure WebView2 async script results can be awaited.
    /// Javascript code is always executed against main window.
    /// Highly inspired by Microsoft.Web.WebView2.Core.DevToolsProtocolExtension.DevToolsProtocolHelper.Runtime.EvaluateAsync (https://docs.microsoft.com/en-us/microsoft-edge/webview2/how-to/chromium-devtools-protocol)
    /// See also https://github.com/MicrosoftEdge/WebView2Feedback/issues/416#issuecomment-1073533384.
    /// </summary>
    internal sealed class WebView2DevTools
    {
        private readonly CoreWebView2 _coreWebView2;

        public WebView2DevTools(CoreWebView2 coreWebView2)
        {
            _coreWebView2 = coreWebView2;
        }

        #region public

        public async Task<object> EvaluateAsync(string jsFunctionCode)
        {
            var callParams = new EvaluateAsyncParameters { Expression = jsFunctionCode };
            var jsonCallParams = JsonConvert.SerializeObject(callParams, GetSerializerSettings());

            // https://chromedevtools.github.io/devtools-protocol/tot/Runtime/#method-evaluate
            var retValJson = await _coreWebView2.CallDevToolsProtocolMethodAsync("Runtime.evaluate", jsonCallParams);

            var retVal = JsonConvert.DeserializeObject<FunctionCallResult>(retValJson);

            ThrowJavascriptErrorIfAny(retVal);

            return retVal.Result.Value;
        }

        #endregion

        #region private

        private JsonSerializerSettings GetSerializerSettings() => new JsonSerializerSettings
        {
            Formatting = Formatting.None,
            NullValueHandling = NullValueHandling.Ignore,
            ContractResolver = new CamelCasePropertyNamesContractResolver()
        };

        private static void ThrowJavascriptErrorIfAny(FunctionCallResult functionCallResult)
        {
            if (functionCallResult.ExceptionDetails == null)
                return;

            throw new InvalidOperationException($"Javascript error: {functionCallResult.ExceptionDetails.Text}");
        }

        #endregion

        #region Json messages and types

        /*
         * Types are defined at https://github.com/ChromeDevTools/devtools-protocol/blob/master/json/js_protocol.json#L2760
         */

        private class Context
        {
            public AuxData AuxData { get; set; }
            public int Id { get; set; }
            public string Name { get; set; }
            public string Origin { get; set; }
            public string UniqueId { get; set; }
        }

        private class ExecutionContextCreatedEventArgs : EventArgs
        {
            public Context Context { get; set; }
        }

        private class RemoteObject
        {
            public string Type { get; set; }
            public string Subtype { get; set; }
            public string ClassName { get; set; }
            public object Value { get; set; }
            public string UnserializableValue { get; set; }
            public string Description { get; set; }
            public string ObjectId { get; set; }
        }

        private class ExceptionDetails
        {
            public int ExceptionId { get; set; }
            public string Text { get; set; }
            public int LineNumber { get; set; }
            public int ColumnNumber { get; set; }
            public string ScriptId { get; set; }
            public string Url { get; set; }
            public int? ExecutionContextId { get; set; }
        }

        private class FunctionCallResult
        {
            public RemoteObject Result { get; set; }
            public ExceptionDetails ExceptionDetails { get; set; }
        }


        private class EvaluateAsyncParameters
        {
            public string Expression { get; set; }
            public string ObjectGroup { get; set; }
            public bool? Silent { get; set; }
            public int? ContextId { get; set; } // If this param is omitted, the evaluation will be performed in the context of the inspected page.
            public bool? ReturnByValue { get; set; } = true;
            public bool? AwaitPromise { get; set; } = true;
            public bool? UserGesture { get; set; }
        }

        private class AuxData
        {
            public string FrameId { get; set; }
            public bool IsDefault { get; set; }
            public string Type { get; set; }
        }

        #endregion
    }
}