Grep a function's source body

example.js

function beep () {
  var b = 2;
  var c = 10;
  var foo = 'foo';
  var biz = foo;
  var str = foo +' '+ biz;
  var sum = b + c;
  return [str, sum];
}

var search = grep(beep, 'str');
var numbered = search.map(function(l, i) { return i +' '+ l; });
var str = numbered.join('\n');

console.log(str);
// 0   var str = foo +' '+ biz;
// 1   return [str, sum]; 

fn-src-grep.js

function grep (fn, pattern) {
 var re = null;
 return (
  fn.toString()
  .split('\n')
  .filter((re = RegExp(pattern), re.test.bind(re)))
 );
}