JavaScript eval() fails with window.external.notify(), works with window.alert()

Question

On WP8, if I execute (1):

Microsoft.Phone.WebBrowser wb;
wb.InvokeScript("eval", "window.external.notify('abc');");

It throws a 'target of invocation returned an error', unknown error, hresult 80020101. But (2)

wb.InvokeScript("eval", "window.alert('abc');");

works fine, and displays the message box.

And (3)

wb.InvokeScript("eval", "( function (){window.external.notify('abc');})();");

Also works fine.

My question is, what is it about window.external.notify() that prevents eval from invoking it directly? It is a function call, like window.alert(), so it should be a valid script. But if there is something special about the unadorned call in 1), then why does the wrapped call in 3) work?

I understand that eval() is the root of all evil, and I have read other SO posts relating to eval() problems with a function definition. (Where would we all be without SO?) But this is clearly a different problem.

Answer 1

I think it is related with context of calling that eval(...).

If you call eval("window.external.notify('abc');"), the script should be called on the global window context.

You can check the context as below to pring the current context:
eval("console.log(this); window.external.notify('abc');")

Then try to test in those 3 ways to check is there any difference about the context.

To specify one context to run, you can use call or apply to set context with first param.