Q:

Combining js files efficiently

So, I have my main custom_js.js as shown below:
(function ($, root, undefined) {    
    $(function () {     
        'use strict';   
             //js goes here

        // Default line End
    }); 
})(jQuery, this);

Now, I have an external js file from blazy lazy load.
I tried to put the code in my custom_js.js as below (by just copying and pasting)
(function ($, root, undefined) {    
    $(function () {     
        'use strict';   
        //blazy v.1.5.1         
            (function(k,f){"function"===typeof.....
        // Default line End
    }); 
})(jQuery, this);

But I am getting an error (that "blazy" was not found).
I am simply trying to consolidate the external js into my custom_js file.
What am I doing wrong?
EDIT:
This is the setup:(Everything in footer)
Using the external js.
  <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.3/jquery.min.js"></script>

  <script type="text/javascript" src="https://raw.githubusercontent.com/dinbror/blazy/master/blazy.min.js"></script>

  <script type="text/javascript" src="http://example.com/js/custom_js.js"></script>

A:

What about pasting it at the end of custom_js.js like that:
(function ($, root, undefined) {    
    $(function () {     
        'use strict';   
             //js goes here

        // Default line End
    }); 
})(jQuery, this);

//blazy v.1.5.1         
(function(k,f){"function"===typeof.....

