https://www.indonesien-tourismus.de/wp-content/themes/indonesia/js/cssrelpreload.js

1/*! loadCSS. [c]2017 Filament Group, Inc. MIT License */
2/* This file is meant as a standalone workflow for
3- testing support for link[rel=preload]
4- enabling async CSS loading in browsers that do not support rel=preload
5- applying rel preload css once loaded, whether supported or not.
6*/
7(function( w ){
8	"use strict";
9	// rel=preload support test
10	if( !w.loadCSS ){
11		w.loadCSS = function(){};
12	}
13	// define on the loadCSS obj
14	var rp = loadCSS.relpreload = {};
15	// rel=preload feature support test
16	// runs once and returns a function for compat purposes
17	rp.support = (function(){
18		var ret;
19		try {
20			ret = w.document.createElement( "link" ).relList.supports( "preload" );
21		} catch (e) {
22			ret = false;
23		}
24		return function(){
25			return ret;
26		};
27	})();
28
29	// if preload isn't supported, get an asynchronous load by using a non-matching media attribute
30	// then change that media back to its intended value on load
31	rp.bindMediaToggle = function( link ){
32		// remember existing media attr for ultimate state, or default to 'all'
33		var finalMedia = link.media || "all";
34
35		function enableStylesheet(){
36			// unbind listeners
37			if( link.addEventListener ){
38				link.removeEventListener( "load", enableStylesheet );
39			} else if( link.attachEvent ){
40				link.detachEvent( "onload", enableStylesheet );
41			}
42			link.setAttribute( "onload", null ); 
43			link.media = finalMedia;
44		}
45
46		// bind load handlers to enable media
47		if( link.addEventListener ){
48			link.addEventListener( "load", enableStylesheet );
49		} else if( link.attachEvent ){
50			link.attachEvent( "onload", enableStylesheet );
51		}
52
53		// Set rel and non-applicable media type to start an async request
54		// note: timeout allows this to happen async to let rendering continue in IE
55		setTimeout(function(){
56			link.rel = "stylesheet";
57			link.media = "only x";
58		});
59		// also enable media after 3 seconds,
60		// which will catch very old browsers (android 2.x, old firefox) that don't support onload on link
61		setTimeout( enableStylesheet, 3000 );
62	};
63
64	// loop through link elements in DOM
65	rp.poly = function(){
66		// double check this to prevent external calls from running
67		if( rp.support() ){
68			return;
69		}
70		var links = w.document.getElementsByTagName( "link" );
71		for( var i = 0; i < links.length; i++ ){
72			var link = links[ i ];
73			// qualify links to those with rel=preload and as=style attrs
74			if( link.rel === "preload" && link.getAttribute( "as" ) === "style" && !link.getAttribute( "data-loadcss" ) ){
75				// prevent rerunning on link
76				link.setAttribute( "data-loadcss", true );
77				// bind listeners to toggle media back
78				rp.bindMediaToggle( link );
79			}
80		}
81	};
82
83	// if unsupported, run the polyfill
84	if( !rp.support() ){
85		// run once at least
86		rp.poly();
87
88		// rerun poly on an interval until onload
89		var run = w.setInterval( rp.poly, 500 );
90		if( w.addEventListener ){
91			w.addEventListener( "load", function(){
92				rp.poly();
93				w.clearInterval( run );
94			} );
95		} else if( w.attachEvent ){
96			w.attachEvent( "onload", function(){
97				rp.poly();
98				w.clearInterval( run );
99			} );
100		}
101	}
102
103
104	// commonjs
105	if( typeof exports !== "undefined" ){
106		exports.loadCSS = loadCSS;
107	}
108	else {
109		w.loadCSS = loadCSS;
110	}
111}( typeof global !== "undefined" ? global : this ) );