Triplebyte Pi Programming Question in Javascript

SergioFernandezTripleByteQuestionMarch2016.js

// Sergio Fernandez made on March 2016
// [email protected]
// www.dominicanvoice.com
// this is my Javascript solution to the TripelByte programming quesion.

// TASK: given a string of number and a target value.
// show all the arithmatic combinaitons of the input numbers that add up to the target value.
// note: the input numbers remain in the order they were inputed.

// For example: 
// f("314159265358", 27182) should print:      

// 3 + 1 - 415 * 92 + 65358 = 27182 
// 3 * 1 + 4 * 159 + 26535 + 8 = 27182 
// 3 / 1 + 4 * 159 + 26535 + 8 = 27182 
// 3 * 14 * 15 + 9 + 26535 + 8 = 27182 
// 3141 * 5 / 9 * 26 / 5 * 3 - 5 * 8 = 27182

// this functions replaces eval.. since Triplebyte said I could not use eval.
 function evaluate(expr) {
  return new Function('return '+expr)();
 }
 
 // this is teh core of the program, it calculates all the combinations of the string
 function calc(expr,input,target) { 
   if (input.length==1) { 
    // I'm not allowed to use eval, so I will use my function evaluate
    //if (eval(expr+input)==target) console.log(expr+input+"="+target);
    if (evaluate(expr+input)==target) document.body.innerHTML+=expr+input+"="+target+"<br>";
   }
   else { 
     for(var i=1;i<=input.length;i++) {
      var left=input.substring(0,i);
      var right=input.substring(i);
      ['+','-','*','/'].forEach(function(oper) {
         calc(expr+left+oper,right,target);
      },this);
     }
   }
 };
 
 // this is a shell function to confirm to triplebytes sugested function name and input
 function f(input,total) {
  calc("",input,total);
 }
  f("314159265",27);
// very slow performance for a large number.. will incorporate web workers to improve performance.
// f("314159265358",27182);