String.prototype.sub_String = function()   
{  
  var subset = [];  
  for (var m = 0; m < this.length; m++)   
  {  
    for (var n = m+1; n<this.length+1; n++)   
    {  
      subset.push(this.slice(m,n));  
    }  
  }  
  return subset;  
};  
  
console.log("dog".sub_String());