Javascript - What problems are associated with declaring a prototypical method of a parent function *inside* the parent function's body?

Stylistically, I prefer this structure:

var Filter = function( category, value ){
  this.category = category;
  this.value = value;

  // product is a JSON object
  Filter.prototype.checkProduct = function( product ){
    // run some checks
    return is_match;
  }

};

To this structure:

var Filter = function( category, value ){
  this.category = category;
  this.value = value;
};// var Filter = function(){...}

Filter.prototype.checkProduct = function( product ){
  // run some checks
  return is_match;
}

Functionally (har har), are there drawbacks to stucturing my code this way? Will adding a prototypical method to a parent function object inside the parent function's body ( i.e. before I even finish my parent function's expression statement ) cause unexpected scoping issues?

I've used the first structure before with success, but I want to make sure I'm not setting myself for a debugging headache, or causing a fellow developer grief and aggravation due to bad coding practices.