Bridge

Separates an object’s interface from its implementation.

• In Bridge pattern, there are two parts Abstraction and Implementation.

• This pattern allows Abstraction and Implementation to be developed independently.

• Client will have only access to the Abstraction part without being concerned about Implementation part.

• Bridge pattern separates the Abstraction hierarchy and Implementation hierarchy in two different layers, so that change in one hierarchy will not affect the development or functionality of another hierarchy.

EX:
 
// input devices
 
var Gestures = function (output) {
    this.output = output;
 
    this.tap = function () { this.output.click(); }
    this.swipe = function () { this.output.move(); }
    this.pan = function () { this.output.drag(); }
    this.pinch = function () { this.output.zoom(); }
};
 
var Mouse = function (output) {
    this.output = output;
 
    this.click = function () { this.output.click(); }
    this.move = function () { this.output.move(); }
    this.down = function () { this.output.drag(); }
    this.wheel = function () { this.output.zoom(); }
};
 
// output devices
 
var Screen = function () {
    this.click = function () { log.add("Screen select"); }
    this.move = function () { log.add("Screen move"); }
    this.drag = function () { log.add("Screen drag"); }
    this.zoom = function () { log.add("Screen zoom in"); }
};
 
var Audio = function () {
    this.click = function () { log.add("Sound oink"); }
    this.move = function () { log.add("Sound waves"); }
    this.drag = function () { log.add("Sound screetch"); }
    this.zoom = function () { log.add("Sound volume up"); }
};

function run() {
 
    var screen = new Screen();
    var audio = new Audio();
 
    var hand = new Gestures(screen);
    var mouse = new Mouse(audio);
 
    hand.tap();
    hand.swipe();
    hand.pinch();
 
    mouse.click();
    mouse.move();
    mouse.wheel();
}

run();

Explanation of Example:

• In our example code the Abstraction represents Input devices and the Implementer represents Output devices.

• Gestures (finger movements) and the Mouse are very different input devices, but their actions map to a common set of output instructions: click, move, drag, etc.

• Screen and Audio are very different output devices, but they respond to the same set of instructions. Of course, the effects are totally different, that is, video updates vs. sound effects.

• The Bridge pattern allows any input device to work with any output device.