A simple way to add whether Array contains a string using JS

The Array type of JS does not have a method to determine whether it contains a certain string. The following code implements this function. Students in need can take a look:

Array.prototype.contains = function(v){
  var b = false;
  for(var i=0;i<this.length;i++){
    if(this[i] == v){
      b = true;
      break;
    }
  }
  return b;
};