x.js

// original: https://gist.github.com/qfox/5652198
// this rewrite tries to use globals for any local vars
// you'll have the burden of extra scopes, but it beats dynamic vars (https://gist.github.com/qfox/5652201)

// step1: change var
var $start_foo;
function start(x){
  $start_foo = 0;

  if (x === 1) $start_foo = 1;
  else if (x === 2) $start_foo = 2;
  else if (x === 3) $start_foo = 3;
  else if (x === 4) $start_foo = 4;
  else $start_foo = 5; 

  return $start_foo;
}

// step2: split up code branches
var $start_foo = {};
function start(x){
  $start_foo = 0;

  if (x === 1) $start_foo = 1;
  else $start1(x);

  return $start_foo;
}
function $start1(x){
  if (x === 2) $start_foo = 2;
  else $start2(x);
}
function $start2(x){
  if (x === 3) $start_foo = 3;
  else $start3(x);
}
function $start3(x){
  if (x === 4) $start_foo = 4;
  else $start_foo = 5; 
}