Ah ok so this is probably the parser equivalent to precompiled queries. Given a fixed query, a specific parse row function is created once and than reused. Thanks!

While I think code generation is certainly the right approach in some examples, I see one problem in this example: As the parser is basically pregenerated using a certain column definition, why does the generated function has an parameter columns? It is simply discarded. So I would say it should rather be:

  var parseRow = new Function('parser', code);