Demonstrate how Angular.js injector works.

mini-injector.js

var FN_ARGS = /^function\s*[^\(]*\(\s*([^\)]*)\)/m;
var FN_ARG_SPLIT = /,/;
var FN_ARG = /^\s*(_?)(\S+?)\1\s*$/;
var STRIP_COMMENTS = /((\/\/.*$)|(\/\*[\s\S]*?\*\/))/mg;

function annotate(fn) {
  var $inject = [],
      fnText,
      argText,
      last;

  fnText = fn.toString().replace(STRIP_COMMENTS, '');
  argText = fnText.match(FN_ARGS)[1];

  argText.split(FN_ARG_SPLIT).forEach(function(arg) {
    arg.replace(FN_ARG, function(all, underscore, name) {
      $inject.push(name);
    });
  });

  return $inject;
}


function createInjector(providers) {
  return function injector(fn, self) {
    var args = [],
        $inject = annotate(fn);

    $inject.forEach(function(arg) {
      args.push(providers[arg]);
    });

    return fn.apply(self, args);
  }
}

var injector = createInjector({
  serviceA: 'hello',
  serviceB: 'world',
});

injector(function(serviceA, serviceB) {
  console.log(serviceA, serviceB); // hello world
});