function define() {...}
  function require() {...}
  define("one", function() { return 1; });
  define("two", function() { return require("one") + require("one"); });
  define("three", function() { return require("two") + require("one"); });
  three = require("three");

--->

  three = 3;

There is a certain irony that now it's possible to do optimisations like that in javascript - a dynamically typed language with almost no compile time guarantees.

Meanwhile java used to have easy static analysis as a design goal (and I think a lot of boilerplate is due to that goal) but the community relies so much on reflection, unsafe access, dynamic bytecode generation, bytecode parsing etc that such an optimisation would be almost impossible to get right.