The Tor Browser / file revision

 function add(a, b, k) {

   var result = a + b;

   return k(result);

 }

 function sub(a, b, k) {

   var result = a - b;

   return k(result);

 }

 function mul(a, b, k) {

   var result = a * b;

   return k(result);

 }

 function div(a, b, k) {

   var result = a / b;

   return k(result);

 }

 function arithmetic() {

   add(4, 4, function (a) {

     // 8

     sub(a, 2, function (b) {

       // 6

       mul(b, 3, function (c) {

         // 18

         div(c, 2, function (d) {

           // 9

           console.log(d);

         });

       });

     });

   });

 }

 // Compile with closure compiler and the following flags:

 //

 //     --compilation_level WHITESPACE_ONLY

 //     --source_map_format V3

 //     --create_source_map code_math.map

 //     --js_output_file    code_math.min.js

 //

 // And then append the sourceMappingURL comment directive to code_math.min.js

 // manually.