Simple Dependency Injector in JavaScript

depInj.js

var DI = function (dependency) {
  this.dependency = dependency;
};

// Should return new function with resolved dependencies
DI.prototype.inject = function (func) {
  var startIdx = func.toString().indexOf('(');
  var endIdx = func.toString().indexOf('{');
  var paramsRaw = func.toString().substr(startIdx, endIdx - startIdx).trim();
  var params = paramsRaw.substr(1, paramsRaw.length -2).replace(/ /g, '').split(',');
  
  if(params.length === 1 && params[0] == '') 
    params = [];
    
  var self = this;
  return function() {
    if(params.length > 0){
      return func.apply(this, params.map(function(itm){ 
        return self.dependency[itm];
      }));
    }else{
      return func();
    }
  }
}