https://increcrazer.github.io/libs/instantpage/instantpage.js

1/*! instant.page v2.0.0 - (C) 2019 Alexandre Dieulot - https://instant.page/license */
2
3let urlToPreload
4let mouseoverTimer
5let lastTouchTimestamp
6
7const prefetcher = document.createElement('link')
8const isSupported = prefetcher.relList && prefetcher.relList.supports && prefetcher.relList.supports('prefetch')
9const isDataSaverEnabled = navigator.connection && navigator.connection.saveData
10const allowQueryString = 'instantAllowQueryString' in document.body.dataset
11const allowExternalLinks = 'instantAllowExternalLinks' in document.body.dataset
12const useWhitelist = 'instantWhitelist' in document.body.dataset
13
14let delayOnHover = 65
15let useMousedown = false
16let useMousedownOnly = false
17if ('instantIntensity' in document.body.dataset) {
18    if (document.body.dataset.instantIntensity.substr(0, 'mousedown'.length) == 'mousedown') {
19        useMousedown = true
20        if (document.body.dataset.instantIntensity == 'mousedown-only') {
21            useMousedownOnly = true
22        }
23    } else {
24        const milliseconds = parseInt(document.body.dataset.instantIntensity)
25        if (!isNaN(milliseconds)) {
26            delayOnHover = milliseconds
27        }
28    }
29}
30
31if (isSupported && !isDataSaverEnabled) {
32    prefetcher.rel = 'prefetch'
33    document.head.appendChild(prefetcher)
34
35    const eventListenersOptions = {
36        capture: true,
37        passive: true,
38    }
39
40    if (!useMousedownOnly) {
41        document.addEventListener('touchstart', touchstartListener, eventListenersOptions)
42    }
43
44    if (!useMousedown) {
45        document.addEventListener('mouseover', mouseoverListener, eventListenersOptions)
46    } else {
47        document.addEventListener('mousedown', mousedownListener, eventListenersOptions)
48    }
49}
50
51function touchstartListener(event) {
52    /* Chrome on Android calls mouseover before touchcancel so `lastTouchTimestamp`
53     * must be assigned on touchstart to be measured on mouseover. */
54    lastTouchTimestamp = performance.now()
55
56    const linkElement = event.target.closest('a')
57
58    if (!isPreloadable(linkElement)) {
59        return
60    }
61
62    linkElement.addEventListener('touchcancel', touchendAndTouchcancelListener, {
63        passive: true
64    })
65    linkElement.addEventListener('touchend', touchendAndTouchcancelListener, {
66        passive: true
67    })
68
69    urlToPreload = linkElement.href
70    preload(linkElement.href)
71}
72
73function touchendAndTouchcancelListener() {
74    urlToPreload = undefined
75    stopPreloading()
76}
77
78function mouseoverListener(event) {
79    if (performance.now() - lastTouchTimestamp < 1100) {
80        return
81    }
82
83    const linkElement = event.target.closest('a')
84
85    if (!isPreloadable(linkElement)) {
86        return
87    }
88
89    linkElement.addEventListener('mouseout', mouseoutListener, {
90        passive: true
91    })
92
93    urlToPreload = linkElement.href
94
95    mouseoverTimer = setTimeout(() => {
96        preload(linkElement.href)
97        mouseoverTimer = undefined
98    }, delayOnHover)
99}
100
101function mousedownListener(event) {
102    const linkElement = event.target.closest('a')
103
104    if (!isPreloadable(linkElement)) {
105        return
106    }
107
108    linkElement.addEventListener('mouseout', mouseoutListener, {
109        passive: true
110    })
111
112    urlToPreload = linkElement.href
113
114    preload(linkElement.href)
115}
116
117function mouseoutListener(event) {
118    if (event.relatedTarget && event.target.closest('a') == event.relatedTarget.closest('a')) {
119        return
120    }
121
122    if (mouseoverTimer) {
123        clearTimeout(mouseoverTimer)
124        mouseoverTimer = undefined
125    }
126
127    urlToPreload = undefined
128
129    stopPreloading()
130}
131
132function isPreloadable(linkElement) {
133    if (!linkElement || !linkElement.href) {
134        return
135    }
136
137    if (urlToPreload == linkElement.href) {
138        return
139    }
140
141    if (useWhitelist && !('instant' in linkElement.dataset)) {
142        return
143    }
144
145    if (!allowExternalLinks && linkElement.origin != location.origin && !('instant' in linkElement.dataset)) {
146        return
147    }
148
149    if (!['http:', 'https:'].includes(linkElement.protocol)) {
150        return
151    }
152
153    if (linkElement.protocol == 'http:' && location.protocol == 'https:') {
154        return
155    }
156
157    if (!allowQueryString && linkElement.search && !('instant' in linkElement.dataset)) {
158        return
159    }
160
161    if (linkElement.hash && linkElement.pathname + linkElement.search == location.pathname + location.search) {
162        return
163    }
164
165    if ('noInstant' in linkElement.dataset) {
166        return
167    }
168
169    return true
170}
171
172function preload(url) {
173    prefetcher.href = url
174}
175
176function stopPreloading() {
177    prefetcher.removeAttribute('href')
178}