Can anyone explain this behaviour of Visual Studio's Javascript intellisense?

Question

While writing a Javascript inheritance function some time ago I noticed some very strange behaviour with intellisense in Visual Studio, that I don't think has been documented elsewhere. I've observed this so far in VS2008 and VS2010, but it could date back earlier for all I know.

Basically, VS appears to be executing a function and making the results available in intellisense.

For example:

function test(obj, member, value) {
    obj[member] = value;
    return obj;
}

function harness() {
    var obj = {};
    test(obj, "firstname", "Jack");
    test(obj, "lastname", "Bauer");
    // If you now type in 'obj.' and wait for intellisense to pop-up you will notice that 'firstname' and 'lastname' will appear as members.
}

For the life of me I can't work out how this is possible with a normal syntax checker -- VS could not possibly know that 'firstname' or 'lastname' was an object member without executing 'test()' as they aren't members until the function is called.

Can anyone suggest an explanation?

Answer 1

VS intellisense does indeed execute the code (pseudo-execute, anyway).

Take a look at this: http://weblogs.asp.net/scottgu/archive/2010/04/08/javascript-intellisense-improvements-with-vs-2010.aspx