Hacking typed javascript

Testing Typed JavaScript

• Use the -noflows command-line option to disable flow analysis. If you’re hacking the type-system, interactions with flow analysis may be a distraction.
  Similarly, use the -pretc command-line option to skip type-checking and instead pretty-print the AST annotated with tagcheck expressions.

• To test with a union-typed expression, you need to use functions:
  

  function(x) /*: Int + Str -> Int */ {
    if (typeof x === "number") {
      return x;
    }
    else {
      return x.length;
    }
  }

  
  The following variant will not work:
  

  var x = /*:upcast Int+Str*/"dummy-string";
    if (typeof x === "number") {
      return x;
    }
    else {
      return x.length;
    }
  }

  
  Above, flow-analysis will determine that the else-branch is unreachable and the type system will signal an error.