facade

The Facade Pattern

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The facade pattern belongs to the category of those design patterns called structural. Its purpose is to give you the option to use only a simplified fraction of a given large functionality. Let say you only have to use some features of an external library, so regarding your needs you can use this pattern and stick a facade in front of the given exposed.

Implementation

One of the most famous facades out there is the JQuery library, which actually hides all the difficulties and the peculiarities the DOM object brings us. A facade like this simplifies the interface in order to work more easily and only with the features we need and not more than that.

// Use your own namespace to keep global scope clean
var myNS = myNS || Object.create(null);

// Let say we have a model with an entity
myNS.Entity = function Entity(x, y) {
  this.x = x;
  this.y = y;
};

// We have also a service managing those entities
myNS.service = function service() {
  const methodA = function methodA(entity) {
    return entity.x + entity.y;
  };

  const methodB = function methodB(entity) {
    return entity.x * entity.y;
  };

  return {
    methodA,
    methodB
  };
}();

// Now let say you need only a fraction of the service
myNS.wrapper = function wrapper() {
  const methodC = function methodC(entity) {
    return myNS.service.methodB(entity);
  };

  return {
    methodC
  };
}();

let e = new myNS.Entity(2, 3);

let r = myNS.wrapper.methodC(e); // 6

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Use Cases

• Calculator

Considerations

Pros

• You can use only a fraction of a given large functionality.
• Fast and easy way for the team to adopt the more simplified API.
• Decouple your code from a given external library by using a facade of it.
• You can add more functionality at any time.

Cons

• Each time you update the library you may update the facade as well.

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