Can you create an object in Javascript without declaring every value, and how?

Question

I want to do the following:

var Room = function(name, north, south, east, west) {
    this.name = name;
    this.north = north;
    this.south = south;
    this.west = west;
    this.east = east;
}

Where north, south, east and west is just a flag saying if there is a door there.

When I create an object I have to do this:

var bedroom = new Room('Bedroom', true, false, false, false);

I was wondering if there is a way so that I can just say which directions have a true value such as:

var bedroom = new Room({
    name: 'Bedroom',
    north: true
});

With south, east, and west becoming false. This way if I were to have say 20 different options I would only have to specify the ones I care about, instead of having a long declarations with a lot of false and '' values and I wouldn't need to remember which order they were suppose to be in (north, south, east, west? or north, east, south, west?),

Answer 1

If you really need separate instance variables for north, south, east and west, I'd suggest something like this where you can pass just the directions that you care about in a space delimited string. This makes the calling code much simpler since you don't have to pass anything for the directions that don't exist.

var Room = function(name, directions) {
    this.name = name;
    this.north = this.south = this.west = this.east = false;
    directions = directions.split(" ");
    directions.forEach(function(item) {
        this[item] = true;
    })
}

var bedroom = new Room('Bedroom', 'north south');

---

Or, your object approach works fine too:

var Room = function(name, directions) {
    this.name = name;
    this.north = this.south = this.west = this.east = false;
    for (var dir in directions) {
        this[dir] = directions[dir];
    }
}

var bedroom = new Room('Bedroom', {north: true, south: true});

---

A third approach is to use flags (often used in C/C++). This allows you to pass an arbitrary number of flags in a single value:

var Room = function(name, directions) {
    this.name = name;
    this.directions = directions;
}

Room.prototype = {
   isNorth: function() { return this.directions & Room.north},
   isSouth: function() { return this.directions & Room.south},
   isWest: function() { return this.directions & Room.west},
   isEast: function() { return this.directions & Room.east},
};

Room.north = 1;
Room.south = 2;
Room.east = 4;
Room.west = 8;

var bedroom = new Room('Bedroom', Room.north | Room.south);