https://foodgps.com/wp-content/themes/paperio/assets/js/background-srcset.js?ver=1.0

1/* BG Srcset 1.0 */
2(function(){
3    'use strict';
4
5    var bgsrcset = function(){
6
7        this.called   = false;
8        this.callonce = true;
9        this.compat();
10    };
11
12    bgsrcset.prototype.init = function(target, callback){
13      //retina bool
14      this.retina = window.devicePixelRatio > 1;
15
16      //storage for our elements
17      this.elements = [];
18
19      //global onload callback for imagery
20      this.callback = typeof callback === 'function' ? callback : function(){};
21
22      //window width, for responsive handling
23      this.curwidth = this.getWidth();
24
25      //get our input and turn it into an element list of some sort
26      var elems = this.gather(target);
27
28      //parse the element input
29      for(var i = 0, l = elems.length; i < l; i++){ this.parse(elems[i]); }
30      //this.set();
31      this.resize();
32    };
33
34    /* -----------* /
35       Fix compatibility issues*
36       *only down to IE8
37    / *----------- */
38
39    bgsrcset.prototype.compat = function(){
40      var d = document;
41      /* check for getElementsByClassName */
42      if(typeof d.getElementsByClassName !== 'function'){
43        d.getElementsByClassName = function(str){
44          return d.querySelectorAll('.' + str);
45        };
46      }
47
48      /* check for .trim() */
49      if (!String.prototype.trim) {
50        String.prototype.trim=function(){return this.replace(/^\s+|\s+$/g, '');};
51      }
52
53      /*------------------------* /
54        Check for Event Listener
55      / *------*/
56      if(!d.addEventListener){
57        this.addEvent = function(elem, evName, fn){
58          elem.attachEvent('on'+evName,function(e) {
59            fn(e || window.event);
60          });
61        };
62      }
63
64    };
65
66    /* -----------* /
67       Gather elements
68    / *----------- */
69    bgsrcset.prototype.gather = function(target){
70      var autotypes = ['HTMLCollection', 'NodeList'];
71      var e = target;
72      var type =  (e.nodeType) ? 'Object' : Object.prototype.toString.call( e ).replace(/^\[object |\]$/g, '');
73
74      var func = 'parse' + type;
75
76      if(autotypes.indexOf(type) > -1){
77          return e;
78      }
79
80      if( this[func] ){
81          return this[func](e);
82      }
83
84      return [];
85    };
86
87    bgsrcset.prototype.parseObject = function( target ) {
88      return (target.nodeType) ? [target] : [];
89    };
90
91    bgsrcset.prototype.parseArray = function( target ) {
92     return target;
93    };
94
95    bgsrcset.prototype.parseString = function( target ) {
96
97      var d = document;
98      var e = target.trim();
99      var sel = e[0];
100      var elems = [];
101
102      switch(true){
103      /* class */
104      case sel === '.':
105        elems = d.getElementsByClassName(e.substring(1));
106        break;
107      /* id */
108      case sel === '#':
109        elems.push(d.getElementById(e.substring(1)));
110        break;
111      /* tag */
112      case /^[a-zA-Z]+$/.test(e):
113        elems = d.getElementsByTagName(e);
114        break;
115      /* unknown */
116      default:
117        elems = [];
118      }
119
120      return elems;
121    };
122
123    /* -----------* /
124       Parse datasrc
125    / *----------- */
126    bgsrcset.prototype.parse = function(obj){
127      //our data to parase
128      var bgss = obj.getAttribute('data-bg-srcset');
129      /* exit if no attribute */
130      if(bgss === null){ return false; }
131
132      /* create new element object */
133      this.elements.push({});
134
135      /* split up sets */
136      var set = bgss.split(',');
137      var attr = '';
138      var curelem = this.elements[this.elements.length - 1];
139
140
141      curelem.node = obj;
142      curelem.srcset = [];
143
144      /* loop through sets to define breakpoints */
145      for(var i = 0, l = set.length; i < l; i++){
146        curelem.srcset.push({});
147        attr = set[i].trim();
148        var attrs = attr.split(' ');
149        var a;
150        var e;
151        var t;
152        /* since we can't know the order of the values, starting another loop */
153        for(var attrc = 0, attrl = attrs.length; attrc < attrl; attrc++){
154          a = attrs[attrc];
155          e = curelem.srcset[i]; //current attribute
156          t = a.length-1;
157          switch(true){
158          case a.trim() === "":

159            //in case of extra white spaces
160            continue;
161          case a[t] !== 'w' && a[a.length-1] !== 'x':
162            e.src = a;
163          break;
164          case a[t] === 'w':
165            e.width = parseInt( a.slice( 0, -1 ) );
166          break;
167          case a[t] === 'x':
168            e.retina = ( parseInt( a.slice( 0, -1 ) ) > 1);
169          break;
170          }
171          if(! e.width ){ e.width = Number.POSITIVE_INFINITY; } //set to the top
172          if(! e.retina ){ e.retina = false; }
173        }
174      }
175    };
176
177    /* -----------* /
178       Set image
179    / *----------- */
180    bgsrcset.prototype.set = function(){
181      for(var i = 0, l = this.elements.length; i < l; i++){
182        this.setSingle(i);
183
184      }
185    };
186
187    bgsrcset.prototype.setSingle = function(id){
188
189      var width = 0,
190        elem = this.elements[id],
191        comparray = [],
192        best = 0,
193        _this = this;
194
195      width = this.getWidth(); //elem.node.offsetWidth;
196
197      elem.srcset = elem.srcset.sort(dynamicSort("width"));
198
199      for(var i = 0, l = elem.srcset.length; i < l; i++){
200        if(elem.srcset[i].width < width){
201        continue;
202        }
203         comparray.push( elem.srcset[i] );
204      }
205      if(comparray.length === 0){
206        comparray.push(elem.srcset[elem.srcset.length -1]);
207      }
208
209      best = comparray[0];
210
211      if(comparray.length > 1 && comparray[0].width === comparray[1].width){
212        best = (comparray[0].retina !== this.retina) ? comparray[1] : comparray[0];
213      }
214
215      if( best.src !== undefined && best.src !== 'null'){
216         var img = new Image();
217          var done = false;
218
219        img.onload = img.onreadystatechange = function() {
220
221            if ( !done && (!this.readyState ||
222                this.readyState === "loaded" || this.readyState === "complete") ) {
223                done = true;
224
225                elem.node.style.backgroundImage = "url('" + best.src + "')";
226
227                /* only fire the callback on initial load, not resize events */
228                if (!_this.called) {
229
230                    _this.callback(elem);
231                    _this.called = _this.callonce;
232
233                }
234
235            }
236
237        };
238
239        img.src = best.src;
240      }else{
241        elem.node.style.backgroundImage = "";
242      }
243
244
245    };
246
247    /* -----------* /
248       Handle Resize
249    / *----------- */
250    bgsrcset.prototype.resize = function(){
251      var _this = this,
252        resizeTimer = setTimeout(function(){}, 0);
253
254       this.addEvent(window, 'resize',function() {
255         clearTimeout(resizeTimer);
256         resizeTimer = setTimeout(function(){
257           var w =  _this.getWidth();
258           if ( w !== _this.curwidth ){
259             _this.curwidth = w;
260             _this.set();
261           }
262         }, 250);
263       });
264    };
265
266    bgsrcset.prototype.addEvent = function(elem, evName, fn){
267      elem.addEventListener(evName,fn,false);
268    };
269
270    bgsrcset.prototype.getWidth = function(){
271        var w, d, e, g;
272        w = window;
273        d = document;
274        e = d.documentElement;
275        g = d.getElementsByTagName('body')[0];
276
277        return w.innerWidth || e.clientWidth || g.clientWidth;
278    };
279
280    function dynamicSort(property) {
281      var sortOrder = 1;
282      if(property[0] === "-") {
283        sortOrder = -1;
284        property = property.substr(1);
285      }
286      return function (a,b) {
287        var result = (a[property] < b[property]) ? -1 : (a[property] > b[property]) ? 1 : 0;
288        return result * sortOrder;
289      };
290    }
291
292    window.bgsrcset = bgsrcset;
293})();
294
295var bgss = new bgsrcset();
296
297bgss.callonce = false;
298
299bgss.init( '.bg-image-srcset' );