Execute function after loading all the scripts in pure Javascript

I'm creating a plugin for Google Chrome where I inject elements into the page like the FontAwesome and Jquery libraries. These elements that I inject are coming from host's CDN's and need to start a function once they are all validated. to do this, I've developed this function:

var fn = {
    injection : {
        fontAwesome : {
            type : 'link',
            attr : {
                rel : 'stylesheet',
                href : 'https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.4.0/css/font-awesome.css'
            },
            insertBefore : 'head',
            check : true
        },
        jquery : {
            type : 'script',
            attr : {
                src : 'https://code.jquery.com/jquery-2.1.4.min.js'
            },
            insertBefore : 'head',
            check : true
        }
    },
    makeInjection : function(){
        var check = 0, obj = this.injection;
        function bootstrapped(){
            if(check == Object.keys(obj).length){
                fn.init();
            };
        }
        for (var param in obj) {
            var el = document.createElement(obj[param].type), ib;
            obj[param].insertBefore == 'head' ? ib = document.head : ib = document.body;
            for (var attr in obj[param].attr) {
                el.setAttribute(attr,obj[param].attr[attr]);
            };
            ib.insertBefore(el, ib.childNodes[ib.childNodes.length]);
            if(obj[param].hasOwnProperty('check')){
                el.onload = function(){
                    setTimeout(function(){
                        check++;
                        bootstrapped();
                    },100);
                }
            } else {
                setTimeout(function(){
                    check++;
                    bootstrapped();
                },100);             
            }
        };
    },
    init : function(){
        console.log('carrego tudo!');
        return $;
    }
}

My problem is that when I run this script alone, without being compiled inside an extension, it works out that it's a beauty, now when I compile it buga and says that jquery is not loaded. Does anyone have a light there?