Include the minified version at the top of any of our .jsx script files and then you can include files from adobe_scripts/lib just by calling Libraries.include("subdir/myscript")

Libraries.jsx

// Assumes that your script is somewhere within a folder called "adobe_scripts" and 
// that you store your includable files relative to `adobe_scripts/lib/`

// indexOf polyfill from https://gist.github.com/atk/1034425
[].indexOf||(Array.prototype.indexOf=function(a,b,c){for(c=this.length,b=(c+~~b)%c;b<c&&(!(b in this)||this[b]!==a);b++);return b^c?b:-1;});

var Libraries = (function (libPath) {    
    return {
        include: function (path) {
            if (!path.match(/\.jsx$/i)) { 
                path = path + ".jsx"; 
            }
            return $.evalFile(libPath + path);
        }
    };
})($.fileName.split("/").splice(0, $.fileName.split("/").indexOf("adobe_scripts") + 1).join("/") + "/lib/");


// Minified version, to include at the top of any .jsx script file

/**
 * Libraries.include(path) -- path must be relative to adobe_scripts/lib/
 * See: https://gist.github.com/jasonrhodes/5286526
 */
[].indexOf||(Array.prototype.indexOf=function(a,b,c){for(c=this.length,b=(c+~~b)%c;b<c&&(!(b in this)||this[b]!==a);b++);return b^c?b:-1;});
var Libraries=function(a){return{include:function(b){return b.match(/\.jsx$/i)||(b+=".jsx"),$.evalFile(a+b)}}}($.fileName.split("/").splice(0,$.fileName.split("/").indexOf("adobe_scripts")+1).join("/")+"/lib/");

Fantastic, thanks!

Hey I'm trying to use this with Illustrator and keep getting the error:

Error 21: Undefined is not an object.
Line 6 -> var Libraries = (function(libpath){

Thank you so much for you time and no pressure, but do you know what's causing this?