curveship

  var foos1 = [] as Foo[],
      foos2 = [] as (Foo | undefined)[];
  
  // ... later
  
  var foo1 = foos1[i],
      foo2 = foos2[i];

  foo1.bar(); // types fine, TS assumes non-undefined
  foo2.bar(); // TS type error, as you haven't checked undef
  if (foo2) foo2.bar(); // types fine, undef excluded