type guards are not working in this case

[bpasero]

I am using the following example that I took directly from the blog post (http://blogs.msdn.com/b/typescript/archive/2014/11/18/what-s-new-in-the-typescript-type-system.aspx)

var x: any = "foo";
if(typeof x === 'string') {
   console.log(x.subtr(1)); // Error, 'subtr' does not exist on 'string'
}
// x is still any here
x.unknown(); // OK

I am not seeing the error or intellisense for the console.log statement.

Are type guards actually supported in this case or only for union types?

[ahejlsberg]

Type guards do not affect variables of type any. This is a fairly recent change, see #1426 and #1433.

@jonathandturner We should probably update the example in the blog post.

[sophiajt]

As per conversation off-line yesterday, I think this should continue to give the more specific type. With simple types like 'string' we have a complete picture of what the user should be able to do in the if-block.

[RyanCavanaugh]

Strong agreement that we should narrow expressions of type any when there is a type guard for a primitive type (typeof x === 'string'), but not in other cases (x instanceof foo).