Simple dependency injection (requires ES5 support)

dependency-injection.js

'use strict';

var inject;
var specify;

(function (root) {

    var depList = {};
    var things  = {};

    var toString = {}.toString;

    function isString(thing) {
        return toString.call(thing) === '[object String]';
    }

    function isUndefined(thing) {
        return typeof(thing) === 'undefined' || thing === null;
    }

    function isFunction(thing) {
        return toString.call(thing) === '[object Function]';
    }


    specify = function specify(name, deps /* optional */, thing) {

        if (arguments.length === 2) {
            thing = deps;
            deps  = [];
        }

        if (!isString(name) || !name.length) {
            throw TypeError();
        }
        if (!Array.isArray(deps)) {
            throw TypeError();
        }
        if (isUndefined(thing)) {
            throw TypeError();
        }
        if (deps.length > 0 && !isFunction(thing)) {
            throw TypeError();
        }

        depList[name] = deps;
        return things[name] = thing;

    };


    inject = function inject(name /* optional */, deps, thing) {

        if (arguments.length === 2) {
            thing = deps;
            deps  = name;
            name  = false;
        }

        if (!Array.isArray(deps)) {
            throw TypeError();
        }
        if (isUndefined(thing)) {
            throw TypeError();
        }
        if (deps.length > 0 && !isFunction(thing)) {
            throw TypeError();
        }

        if (name) {
            specify(name, deps, thing);
        }

        var injectedDeps = deps.map(function (name) {
            var dep = things[name];
            if (isFunction(dep)) {
                return inject(depList[name], dep);
            }
            return dep;
        });

        return thing.apply(root, injectedDeps);

    };

}).call(this);

example.js

specify('singleton-example', {
  x: 100,
  y: 200,
  name: 'example'
});

specify('service-example', ['singleton-example'], function (singleton) {
  var store = {};
  return {
    set: function (name, str) {
      store[name] = str;
    },
    get: function (name) {
      return 'example ' + store[name];
    }
  }
});

inject('inject-example', ['service-example'], function (exmaple) {
  example.set('test', 'test');
  console.log(example.get('test')); // 'example test'
});