let's call it an mvp

example.txt

$ npm i esprima falafel
$ node sib.js | node
{ '4': [ [ 2, 'big' ], [ 2, 'big' ] ],
  '8': [ [ 6, 'little' ] ],
  '11': [ [ 11, 'big' ], [ 11, 'little' ] ] }

lol.js

var x;
x = sth(
  true
);

var y = sth(
  false
);

function sth(big) {
  return big ? 'big' : 'little';
}

sib.js

var esprima = require('esprima'),
    falafel = require('falafel');

var src = require('fs').readFileSync('./lol.js', 'utf8');

var transformed = falafel(src, { loc: true }, function(node) {
  var loc = node.loc;
  if (node.type.match(/Expression$/))
    node.update('(__jsib.record(' + loc.end.line + ',' + loc.start.line + ',(  ' + node.source() + '  )))');

});

var output =
      "(function() {var __jsib={r:{}}; __jsib.record = function(end,start,val){(this.r[end] = this.r[end] || []).push([start, val]); return val;};\n\n" +
      transformed + "\n\n" +
      "console.dir(__jsib.r); return __jsib.r;})();";
console.log(output);