Type narrowing is not allowed if variable is reassigned after the use site inside if block #1764

Current implementation is very conservative when looking for assignments during application of type narrowing.

function len(x: number | string) {
     if (typeof x === 'number') {
         var t = x.toExponential();
         //x = "aaaa"; // uncomment me
     }
}

variable is reassigned after the usage of narrowed type but type narrowing still not kicked in