Get Bachelor - return odd occurrence in array

get_bachelor.js

(function(input){

function solution(A){
  var input = (function(bachelor){
    if (typeof A !== "object") throw new Error("A is not an object.");
    if (typeof A.split === "function") throw new Error("A is not an array.");
    if (!(A.length % 2)) throw new Error("A.length even.");
    return {
      squashCouples: function(lookup){
        lookup = {};
        A.map(function(val){
          val = val.toString();          
          if (!lookup[val]){
            lookup[val] = true;
          } else {
            delete(lookup[val]);
          }
        });
        A = lookup;
        return this;
      },
      getBachelor: function(){
        return parseInt(Object.keys(A).pop());
      }
    };
  })();

  return input
    .squashCouples()
    .getBachelor();
}

return solution(input);