I’ve had several discussion recently some of the more advanced features of JavaScript, such as functions as return values, namespaces, encapsulation, etc. In order to demonstrate some of these things, I contrived a simple example of a dependency injection tool.
Never mind that dependency injection is not really a relevant pattern in JavaScript or other dynamic languages. It just fit all the pieces I wanted to demo. The Rhino JavaScript engine was used to run and test the example.
For more on how this stuff works, check out Douglas Crockford’s JavaScript: The Good Parts
//ObjectMap namespace
var ObjectMap = function (){
var that = this;
that.container = function () {
var registry = {};
var fact = {};
fact.register = function (name, constructor) {
registry[name] = constructor;
};
fact.getObject = function (theType) {
return registry[theType]();
};
return fact;
}();
return that;
}();
//Dog constructor, with encapsulated private name
var Dog = function () {
var d = {};
var name = "spot";
d.getName = function () {return name;};
d.setName = function (val) {name=val; return d;};
d.speak = function () {return d.getName() + " barks";};
return d;
};
//register Dog with the DI tool
ObjectMap.container.register("Dog", Dog);
//get and use an object function the DI tool
var munson = ObjectMap.container.getObject("Dog");
munson.setName("Munson");
print(munson.speak());
