javascript array.contains and array.diff

gistfile1.js

Array.prototype.contains = function(val, eqFunc /* (val, arrVal) */){
  eqFunc = eqFunc || function(val1, val2){return val1 == val2;};

  for(var i = 0; i < this.length; i++){
    if(eqFunc(val, this[i])){
      return true;
    }
  }
  
  return false;
};

Array.prototype.diff = function(arr2, eqFunc){
  var arr1 = this;
  var res = [];
  for(var i = 0; i < arr1.length; i++){
    if(!arr2.contains(arr1[i], eqFunc)){
      res.push(arr1[i]);
    }
  }
  
  return res;
};