di-lite

A ultra light-weight dependency injection container in Javascript

di-lite.js

di-lite is designed to act as a minimalistic dependency injection container in Javascript. It has no dependency on any other framework such as CommonJs or RequireJs in contrary to some of other more heavy weight DI container implementation on the web.

di-lite was initially extracted from a Backbone.js based application. In this application, RequireJs was used to wire dependencies at module level. Each module could contain multiple views and models. We found using RequireJs to wire every individual view and model is a bit of overkill and verbose, however we still want the inversion of control to keep our code nicely isolated and testable. That's the reason behind the creation of this lightweight container implementation - to provide dependencies injection at sub-modular level.

That being said di-lite is designed to be used standalone there is no dependency on Backbone or RequireJs. Its a fully functional dependency injection container by itself while extremely lightweight and works well both in browser or node.

npm install di-lite

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var A = function(){
    ...
    this.dependencies = "b, c";
    ...
};
var B = function(){
    ...
    this.dependencies = "c";
    ...
};
var C = funciton(){...};
 
// create di context 
var ctx = di.createContext();
 
// register a class with an unique name 
ctx.register("a", A);
ctx.register("b", B);
ctx.register("c", C);
 
// initialize di container so all singleton(default) objects will be wired at this stage 
ctx.initialize();
 
var instanceOfA = ctx.get("a");
instaceOfA.=== ctx.get("b"); // true 
instaceOfA.=== ctx.get("c"); // true 
 
var instanceOfB = ctx.get("b");
instanceOfB.=== ctx.get("c"); // true 

By default dependencies are wired using their registered name respectively, however you can override this behavior by including an explicit assignment in dependency definition. You can also mix both explicit and implicit assignment in dependency definition.

var A = function(){
    ...
    this.dependencies = "bee=b, c"; // mix explicit and implicit assignment 
    ...
};
 
ctx.initialize();
 
var instanceOfA = ctx.get("a");
instaceOfA.bee === ctx.get("b"); // true - explicit assignment 
instaceOfA.=== ctx.get("c"); // true - implicit assignment 

di-lite container resolves dependency passively on demand when get() method is invoked. It only tries to resolve dependency for this particular object thus only traverse its sub-dependency-tree. initialize() call does resolve all dependencies for all registered objects however it is actually optional (though recommended to guarantee).

ctx.register("a", A);
ctx.get("a"); // this triggers the dependency resolution for "a" alone 
ctx.initialize(); // this triggers the dependency resolution for everyone registered 

All objects created and managed by di-lite.js container are by default singleton.

ctx.get("a") === ctx.get("a"); // true 

If you want container to create a new instance of your class each time you invoke get method then you need to configure your registration with di.strategy.proto cache strategy.

ctx.register("prototype", A).strategy(di.strategy.proto);
ctx.get("prototype") === ctx.get("prototype"); // false 
ctx.create("prototype", 100); // create can be used if you want to explicitly pass in a new parameter 

You can pass arguments to constructor function by using the additional parameter in register call.

ctx.register("str", String, "hello world"); // signle simple argument 
ctx.register("profileView", ProfileView, {el: "#profile_div"}); // signle object literal argument 
ctx.register("array", Array, ["Saab","Volvo","BMW"]); // multiple argument is passed in using an array 

di-lite.js container supports solution of cyclical dependencies, so the following dependency relationship is valid.

var A = function(){
    ...
    this.dependencies = "b";
    ...
};
var B = function(){
    ...
    this.dependencies = "a";
    ...
};
 
ctx.register("a", A);
ctx.register("b", B);
 
ctx.initialize();
 
ctx.get("a").=== ctx.get("b"); // true 
ctx.get("b").=== ctx.get("a"); // true 
ctx.get("a").b.=== ctx.get("a"); // true 
ctx.get("b").a.=== ctx.get("b"); // true 

What if your are using functional object pattern and do not have a constructor function for your object? di-lite.js fully supports functional object pattern since we believe this is the best way to create javascript object anyway.

var FuncObject = function(spec){
    var that = {};
    ...
    return that;
};
 
ctx.register("funcObjSingleton", FuncObject, spec).factory(di.factory.func);
 
// function chaining can be used to customize your object registration 
ctx.register("funcObjProto", FuncObject, spec)
    .strategy(di.strategy.proto)
    .factory(di.factory.func);
 
ctx.initialize();
 
ctx.get("funcObjSingleton"); // will return you a signleton instance of FuncObject 
ctx.get("funcObjProto"); // will return you a new instance of FuncObject each time 

di-lite container provides a lifecycle hook callback ready if the wired object provide a ready function then the callback will be executed once all dependencies are satisfied.

var MyView = Backbone.View.extend({
    ...
    dependencies: "otherView, myModel",
    readyfunction(){this.render();} // called once all dependencies are satisfied 
    ...
});

What if I need to provide different dependencies different instances of the same class?

ctx.register("a", A)
    .dependencies("bee=b"); // dependencies specified here will take precedence 
...
ctx.get("a").bee === ctx.get("b"); // true 

Sometimes you just don't have control over the object you want to wire or maybe you need to create the object and initialize before anything else is create or even registered. You can manually insert object into di-lite container and control the whole creation process this way.

ctx.register("history").object(Backbone.history);
...
ctx.get("history").start(); // you can use it since it is already created and initialized 
...
ctx.initialize(); // initialize the rest of the objects 

Make sure the following packages are installed on your machine

  • node.js
  • npm
  • apache ant

di-lite$ npm install

di-lite$ ./make

di-lite is an open source javascript library and licensed under Apache License v2.