https://maritiemdigitaal.nl/_content/DDigit.BlazorComponents/js/virtual.8tkzxgfm05.js

1class VirtualList {
2  constructor(objRef, id) {
3    this.objRef = objRef;
4    this.initIntersectionObserver(id);
5  }
6
7  initIntersectionObserver(id) {
8    if (this.observer) {
9      this.dispose();
10    }
11
12    this.element = document.getElementById(id);
13    if (this.element != null) {
14      this.children = Array.from(this.element.querySelectorAll('.virtual-item'));
15      this.visibleItems = new Set();
16      const options = {
17        threshold: 0.1
18      };
19
20      this.observer = new IntersectionObserver(this.handleIntersect.bind(this), options);
21      this.children.forEach((child, index) => {
22        child.dataset.index = index;
23        this.observer.observe(child)
24      });
25    }
26  }
27
28  handleIntersect(entries) {
29    entries.forEach(entry => {
30        const index = parseInt(entry.target.dataset.index);
31
32        if (entry.isIntersecting) {
33          this.visibleItems.add(index);
34        }
35        else {
36          this.visibleItems.delete(index);
37        }
38      });
39
40    clearTimeout(this.debounceTimeout);
41    this.debounceTimeout = setTimeout(() => {
42        this.objRef.invokeMethodAsync('UpdateVisibleItems', Array.from(this.visibleItems));
43      }, 150);
44  }
45
46  dispose() {
47    if (this.observer) {
48      this.observer.disconnect();
49      this.observer = null;
50    }
51
52    if (this.debounceTimeout) {
53      clearTimeout(this.debounceTimeout);
54      this.debounceTimeout = null;
55    }
56
57    this.visibleItems.clear();
58    this.children = null;
59    this.element = null;
60  }
61}
62
63window.InitializeVirtualList = function(objRef, id) {
64  const list = new VirtualList(objRef, id);
65  window.virtualLists[id] = list;
66}
67
68window.UpdateVirtualList = function(id) {
69  window.virtualLists[id].initIntersectionObserver(id);
70}
71
72window.DisposeVirtualList = function(id) {
73  if (window.virtualLists[id]) {
74    window.virtualLists[id].dispose();
75    window.virtualLists[id].objRef = null;
76    delete window.virtualLists[id];
77  }
78}
79
80window.virtualLists = {};