$async(
   [/*stylesheets*/],     // string, object or an array of strings or objects
   {/*options*/},         // object
   [/*capture*/],         // string, object or an array of strings or objects 
   {/*capture options*/}  // object
).then(function() { /* ready */ });
​
// alternative load method for chaining when using the API module
$async.load(/*...*/).load(/*...*/).then(/*...*/)
​
// custom timing when using the API module
$async.time(
  {/*timing config*/},
  function() {
    // script
  },
  [/*optional debug-info*/]
);

// simple async loading
$async('sheet.css').then(function() { /* onload */ });

// dependencies, timing and global options
$async(
   [  // load 3 stylesheets
      'sheet.css', 
      {
         href:'other-sheet.css',
         dependencies: ['sheet.css'], // wait for sheet.css via dependencies and insert after DOM element
         load_timing: {
            type: 'inview',
            selector: '#footer', // download stylesheet when footer becomes visible within 250 pixels
            offset: -250
         }
      }, 
      {
         href:'mobile-sheet.css',
         target: {
            after: 'meta[charset]'
         },
         load_timing: {
            type: 'media', // download stylesheet based on a media query (also works with viewport changes)
            media: 'screen and (max-width: 600px)'
         }
      }
   ],
   {  // global options applied to all stylesheets
      base: '/long/path/to/css/', // base directory for relative sheet URLs
      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
         },
         source: ['cssText','xhr','cors'], // default
         cors: {
            proxy: 'https://cors-anywhere.herokuapp.com/', // more proxies on https://gist.github.com/jimmywarting/ac1be6ea0297c16c477e17f8fbe51347
         },
         xhr: {
            headers: {
               "x-special-header": "secret-key" // request header to include in XHR requests
            }
         }
      },
      attributes: { 
         "data-app-sheet": "1" // HTML attribute to add to stylesheet element
      },
      render_timing: 'requestAnimationFrame' // render via requestAnimationFrame
   } 
).then(function() { /* ready */ });

// chainable
$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');

{
  "href": "sheet.css",
  "dependencies": [
    "other-sheet.css"
  ],
  "cache": {
    "type": "localstorage",
    "max_size": 10000,
    "fallback": "cache-api",
    "update": {
      "head": true,
      "interval": 86400
    },
    "source": "cors",
    "cors": {
      "proxy": "https://cors-anywhere.herokuapp.com/"
    },
    "xhr": {
      "headers": {
        "x-special-header": "secret-key"
      }
    }
  },
  "attributes": {
    "data-app-sheet": "1"
  },
  "load_timing": {
    "type": "inview",
    "selector": "#footer",
    "offset": -250
  },
  "render_timing": "requestAnimationFrame"
}

// preload popup script in background
$async.js({
    "ref": "popup",
    "dependencies": "jquery",
    "load_timing": "domReady",
    "exec_timing": {
        "type": "method",
        "method": "exec_popup_script"
    }
});
​
// just-in-time
jQuery('button.popup').on('click', function() {
​
    // load popup script
    exec_popup_script().then(function() {
      alert('popup script ready');
    });
});

$async(
  ["sheet1.css", {"href":"sheet2.css", "ref": "test"}], 
  // global options applied to sheet1.css and sheet2.css
  // ref from sheet2.css overrides the global ref
  {
    "ref": "global-options",
    "load_timing": "domReady"
});

$async.time(
  {
     "type": "requestIdleCallback",
     "timeout": 3000
  },
  function() {
    // big script
  },
  ["big-script"]
);

$async.time({"2":53,"57":3000},function(){}); // 3000ms timeout

$async.time("requestIdleCallback", function() {});
$async.time(53, function() {}); // compression index