$async([
   'sheet.css',
   'script.js'
]).then(function() { /* ready */ });

$async
   .on('load',function(sheet, sheetEl){
      //  sheet.css or other-sheet.css loaded
   }) 
   .on('sheet-ref',function() { }) // sheet with ref-name loaded
   .on('sheet.css', function() {}); // sheet with href loaded
   .load({
      href: 'sheet.css', 
      ref: 'sheet-ref'
   })
   .then(function() { }) // sheet.css loaded
   .load('other-sheet.css');

$async(
   [
      "sheet.css",
      {
         href:"other-sheet.css",
         dependencies: ["sheet.css"], // wait for sheet.css via dependencies
         load_timing: {
            type: "lazy", // use $lazy for timing (Intersection Observer)
            config: [".selector-in-view", 0, "200px"], // visible within 200 pixels
         },
         ref: "other"
      }, 
      {
         href:"mobile-sheet.css",
         dependencies: "other", // dependency by ref
         target: {
            after: "meta[charset]" // control insert target
         },
         load_timing: {
            type: "media", // download stylesheet based on a media query (works with viewport changes, e.g. viewport rotate)
            media: "screen and (max-width: 600px)"
         }
      },
      {
         inline: "inline_script_with_timing_and_dependency();",
         ref: "inline-code"
      },
      {
         src: "script.js",
         exec_timing: "requestIdleCallback",
         dependencies: "inline-code"
      }
   ],
   /* global options: applied to all stylesheets */
   {
      // base directory for relative sheet URLs
      base: "/long/path/to/css/",

      // render timing: paint sheet with requestAnimationFrame
      render_timing: "requestAnimationFrame"
   } 
)
.then(function() { /* ready */ });

$async(
   {
      href:"popup-css.css",
      load_timing: {
         type: "method", // trigger download using custom javascript method
         method: "load_popup_css"
      }
   },{
      src:"popup-script.js",
      load_timing: {
         type: "method",
         method: "load_popup_js"
      }
   }
);

// just-in-time loading
jQuery('button.popup').on('click', function() {

   // user clicks a button
   // load popup script/css just-in-time

    load_popup_css().then(function() {
      alert('popup CSS loaded');
    });

    load_popup_js().then(function() {
      alert('popup script loaded');
    });
});

// dependency resolver
$async.dependencies(['name'], function() { /* dependency loaded */ });

// timing method
$async.time("requestAnimationFrame", function() { /* callback */ });
$async.time(48, function() {}); // the same using the JSON compression index key for 'requestAnimationFrame'

$async({
   href: "sheet.css",
   cache: {
      type: "localstorage",
      max_size: 10000, // cache only <10kb
      fallback: "cache-api", // fallback to Cache-API for bigger sheets
      update: {
         head: true, // use HTTP HEAD request to check for 304 - Not Modified
         interval: 86400 // update once per day
      },

      // control the source methods
      source: ["cssText","xhr","cors"], // default

      // optional: CORS proxy for retrieving the source code from external stylesheet URLs
      cors: {
         proxy: "https://cors-anywhere.herokuapp.com/", // more proxies on https://gist.github.com/jimmywarting/ac1be6ea0297c16c477e17f8fbe51347
      },

      // custom XHR config
      xhr: {
         headers: {
            "x-special-header": "secret-key" // request header to include in XHR requests
         }
      }
   }
});

/* original config: 
{
   "href":"other-sheet.css",
   "dependencies": ["sheet.css"],
   "load_timing":{
      "type":"lazy",
      "config": [".selector-in-view",0,"200px"]
   },
   "ref":"other"
} */

// compressed
$async({"4":"other-sheet.css","15":["sheet.css"],"16":"other","48":{"2":62,"89":[".selector-in-view",0,"200px"]}});

// capture and remove async script-injected sheet
$async.capture(
   [
      {
         match: "bloated-sheet.css",
         action: {
            "type": "remove"
         }
      },
      {
         match: "/<script[^>]+bloated-script-id[^>]+>/",
         regex: true,
         match_type: "node",
         action: {
            "type": "remove"
         }
      },
      {
         match: "external-widget.com",
         action: {
            type: "rewrite",
            search: '/^.*cdn\.external-widget\.com/(.*).css$',
            regex: true,
            replace: "/local-nginx-proxy/$1.css",
            async: {
               "load_timing": "requestIdleCallback",
               "target": {
                  "after": "media[charset]"
               },
               "attributes": {
                  "data-cdn": "external-widget.com"
               }
            }
         }
      },
      {
         match: "customer-review.js",
         action: {
            async: { 
               "load_timing": {
                  type: 'lazy',
                  config: '#customer-review' // load script when customer review widget enters viewport
               }
            }
         }
      }
   ],
   {
      insert: true // use DOM insert method rewriting
      // observer: true // alternative: use MutationObserver
   }
);