// We require a custom configuration with JavaScript
var config = Configuration.Default.WithJs();
// This is our sample source, we will set the title and write on the document
var source = @"<!doctype html>
Sample
";
var document = BrowsingContext.New(config).OpenAsync(m => m.Content(source)).Result;
// Modified HTML will be output
Console.WriteLine(document.DocumentElement.OuterHtml);
```
**Expected behavior:**
Oputput: (in browser)
```html
Simple manipulation...
dGVzdA==
```
**Actual behavior:**
Output:
```html
Simple manipulation...
```
**Environment details:** [Win 10, .NET Framework 4.6.2]
It maybe an obvious question as I don't know the way the library works till now, or just don't know the right way to use it.
### Note
- To get the javascript error append these lines:
```csharp
var service = new JsScriptingService();
var result = service.EvaluateScript(document, "btoa('test')");
Console.WriteLine(result);
```
- **Exception:** System.Reflection.TargetException: 'Object does not match target type.'
generated in [EngineExtensions](https://github.com/AngleSharp/AngleSharp.Js/blob/master/src/AngleSharp.Js/Extensions/EngineExtensions.cs#L205) (Call method).
- When appending these lines:
```csharp
var service = new JsScriptingService();
var result = service.EvaluateScript(document, "btoa");
Console.WriteLine(result);
```
Appended output:
```js
function btoa() { [native code] }
```
So, it exists but I can't call it, maybe I'm using it the wrong way.
Description
btoa() and atob() methods are not working despite they're declared here WindowBase64.cs
Steps to Reproduce
// This is our sample source, we will set the title and write on the document var source = @"<!doctype html>