https://pupwife.com/scripts/effects/scriptLoadOnce.js

1/**
2 * Deduped script loader — prevents parallel duplicate <script src> loads (race → false onerror).
3 */
4(function (global) {
5    'use strict';
6
7    var inflight = Object.create(null);
8    var loaded = Object.create(null);
9
10    function scriptTypeAttr(opts) {
11        return opts && opts.type === 'module' ? 'module' : '';
12    }
13
14    function findExistingScript(src, typeAttr) {
15        var existing = document.querySelector('script[src="' + src + '"]');
16        if (!existing) return null;
17        var existingType = existing.getAttribute('type') || '';
18        if (existingType === typeAttr) return existing;
19        return null;
20    }
21
22    function loadScriptOnce(src, opts) {
23        opts = opts || {};
24        var markKey = opts.markKey || 'spaLoaded';
25        var typeAttr = scriptTypeAttr(opts);
26
27        if (!src) return Promise.resolve();
28        var loadKey = typeAttr ? src + '|' + typeAttr : src;
29        if (loaded[loadKey]) return Promise.resolve();
30        if (inflight[loadKey]) return inflight[loadKey];
31
32        inflight[loadKey] = new Promise(function (resolve, reject) {
33            var existing = findExistingScript(src, typeAttr);
34            if (existing) {
35                if (existing.dataset[markKey] === '1') {
36                    loaded[loadKey] = true;
37                    resolve();
38                    return;
39                }
40                if (existing.dataset[markKey] === 'error') {
41                    reject(new Error('Failed to load ' + src));
42                    return;
43                }
44                function onLoad() {
45                    existing.dataset[markKey] = '1';
46                    loaded[loadKey] = true;
47                    resolve();
48                }
49                function onError() {
50                    existing.dataset[markKey] = 'error';
51                    reject(new Error('Failed to load ' + src));
52                }
53                existing.addEventListener('load', onLoad, { once: true });
54                existing.addEventListener('error', onError, { once: true });
55                global.setTimeout(function () {
56                    if (existing.dataset[markKey] === '1' || existing.dataset[markKey] === 'error') {
57                        return;
58                    }
59                    onLoad();
60                }, 0);
61                return;
62            }
63
64            var script = document.createElement('script');
65            script.src = src;
66            script.async = false;
67            if (typeAttr) script.type = typeAttr;
68            script.onload = function () {
69                script.dataset[markKey] = '1';
70                loaded[loadKey] = true;
71                delete inflight[loadKey];
72                resolve();
73            };
74            script.onerror = function () {
75                script.dataset[markKey] = 'error';
76                delete inflight[loadKey];
77                reject(new Error('Failed to load ' + src));
78            };
79            (opts.parent || document.body).appendChild(script);
80        });
81
82        return inflight[loadKey].catch(function (err) {
83            delete inflight[loadKey];
84            throw err;
85        });
86    }
87
88    function forgetScript(src, opts) {
89        opts = opts || {};
90        var typeAttr = scriptTypeAttr(opts);
91        var loadKey = typeAttr ? src + '|' + typeAttr : src;
92        delete loaded[loadKey];
93        delete inflight[loadKey];
94    }
95
96    global.PupwifeScriptLoad = {
97        once: loadScriptOnce,
98        forget: forgetScript
99    };
100})(typeof window !== 'undefined' ? window : this);