Prefix to Infix Mathematical Conversion and Execution

preInfix.js

/**
 *  Author: Tyson Bruhn
 *
 *  @func
 *  @param {String} prefix The initial prefix string.
 *  @return {[String, Float]} An array with the infix string and the mathematical solution
 *  @example
 *      preInfix("+52-3"); //=> "["(5+2)-3",4]"
**/

function preInfix(prefix){
  var prefixchars = prefix.split("").reverse();

  var nums = [];
  var total = 0;
  var infix = "";
  var expressions = [];

  prefixchars.map(
    function(character){
      if(character === '+' || character === '-' || character === '*' || character === '/'){
        // if operator
        if(nums.length < 1){
          infix = getInfixForOperation(character, expressions.reverse(),"");
          expressions = [];
        } else if (nums.length === 1){// if there is only one number
          expressions.push(character + nums[0]);
          nums = [];
        } else {
          expressions.push(getInfixForOperation(character, nums.reverse(), '(' + infix ) + ')' );
          nums = [];
        }
      } else {
        // if number
        nums.push(character);
      }
    }
  );

  if(expressions.length > 0) {
    infix = getInfixForOperation("", expressions.reverse(),"");
  }

  function getInfixForOperation(character, nums, str){
    for(var i = 0; i < nums.length-1; i++){
      str = str + nums[i] + character;
    };
    return str + nums[nums.length-1];
  }

  return [infix, eval(infix)];
}

/** Tests **/

/* Stated Test Case */
assertEqualArrays("Infix with one layer", preInfix("+57-3"),["(5+7)-3",9]);

/* Test Remainder Case where the number of remaining space cannot be evenly distrubted between words */
assertEqualArrays("Two layer infix ", preInfix("-+57-53"),["(5+7)-(5-3)",10]);

assertEqualArrays("Two layer infix ", preInfix("-+572-532"),["(5+7+2)-(5-3-2)",14]);

/** Test helper **/
function assertEqual(z,x,y){
    if(x!==y) throw(z + " expected " + x + "to equal " + y);
}

function assertEqualArrays(z,x,y){
  if(x.length !== y.length) throw(z + " expected " + x + " to equal " + y);
  for(var i in x) {
    if(x[i] !== y[i]) {
        throw(z + " expected " + x +" to equal " + y);
    }
  }
}

console.log("All test cases ran successfully");