js設計模式之Structural Patterns------Bridge(2)

The bridge pattern takes the adapter pattern to a new level. Given an interface, we
can build multiple adapters, each one of which acts as an intermediary to a different
implementation.

The first thing we need is a number of different gods to which we can pray:

class OldGods{
    prayTo(sacrifice){
        console.log("We Old Gods hear your prayer");
    }
}
Religion.OldGods = OldGods;
class DrownedGod {
    prayTo(humanSacrifice) {
        console.log("*BUBBLE* GURGLE");
    }
}
Religion.DrownedGod = DrownedGod;
class SevenGods {
    prayTo(prayerPurpose){
        console.log("Sorry there are a lot of us, it gets confusing here. Did you pray for something");
    }
}
Religion.SevenGods = SevenGods;

You may notice, however, that the signature for the prayTo method for each religion is
slightly different. This proves to be something of an issue when building a consistent
interface like the one shown in pseudo code here:

interface God
{
  prayTo():void;
}

So let’s slot in a few adapters to act as a bridge between the classes we have and the
signature we would like the following:

class OldGodsAdapter {
    constructor(){
        this._oldGods = new OldGods();
    }
    prayTo() {
        let sacrifice = new Sacrifice();
        this._oldGods.prayTo(sacrifice);
    }
}
Religion.OldGodsAdapter = OldGodsAdapter;
class DrownedGodAdapter {
    constructor() {
        this._drownedGod = new DrownedGod();
    }
    prayTo() {
        let sacrifice = new HumanSacrifice();
        this._drownedGod.prayTo(sacrifice);
    }
}
Religion.DrownedGodAdapter = DrownedGodAdapter;
class SevenGodsAdapter {
    constructor(){
        this.prayerPurposeProvider = new PrayPurposeProvider();
        this._sevenGods = new SevenGods();
    }
    prayTo() {
        this._sevenGods.prayTo(this.prayerPurposeProvider.GetPurpose());
    }
}
Religion.SevenGodsAdapter = SevenGodsAdapter;
class PrayerPurposeProvider {
    GetPurpose (){}
}
Religion.PrayerPurposeProvider = PrayerPurposeProvider;

Each one of these adapters implements the God interface we wanted and abstracts
away the complexity of dealing with three different interfaces, one for each god:
To use the Bridge pattern, we could write code like so:

let god1 = new Religion.SevenGodsAdapter();
let god2 = new Religion.DrownedGodAdapter();
let god3 = new Religion.OldGodsAdapter();

let gods = [god1,god2,god3];
for (let i =0; i<gods.length; i++){
    gods[i].prayTo();
}

Because there are no interfaces in JavaScript, the bridge pattern is far closer to the adapter in JavaScript than in other languages. In fact, it is basically exactly the same.