1 | const support = function(feature) {
|
2 | if (typeof document === `undefined`) {
|
3 | return false
|
4 | }
|
5 | const fakeLink = document.createElement(`link`)
|
6 | try {
|
7 | if (fakeLink.relList && typeof fakeLink.relList.supports === `function`) {
|
8 | return fakeLink.relList.supports(feature)
|
9 | }
|
10 | } catch (err) {
|
11 | return false
|
12 | }
|
13 | return false
|
14 | }
|
15 |
|
16 | const linkPrefetchStrategy = function(url) {
|
17 | return new Promise((resolve, reject) => {
|
18 | if (typeof document === `undefined`) {
|
19 | reject()
|
20 | return
|
21 | }
|
22 |
|
23 | const link = document.createElement(`link`)
|
24 | link.setAttribute(`rel`, `prefetch`)
|
25 | link.setAttribute(`href`, url)
|
26 |
|
27 | link.onload = resolve
|
28 | link.onerror = reject
|
29 |
|
30 | const parentElement =
|
31 | document.getElementsByTagName(`head`)[0] ||
|
32 | document.getElementsByName(`script`)[0].parentNode
|
33 | parentElement.appendChild(link)
|
34 | })
|
35 | }
|
36 |
|
37 | const xhrPrefetchStrategy = function(url) {
|
38 | return new Promise((resolve, reject) => {
|
39 | const req = new XMLHttpRequest()
|
40 | req.open(`GET`, url, true)
|
41 | req.withCredentials = true
|
42 |
|
43 | req.onload = () => {
|
44 | if (req.status === 200) {
|
45 | resolve()
|
46 | } else {
|
47 | reject()
|
48 | }
|
49 | }
|
50 |
|
51 | req.send(null)
|
52 | })
|
53 | }
|
54 |
|
55 | const supportedPrefetchStrategy = support(`prefetch`)
|
56 | ? linkPrefetchStrategy
|
57 | : xhrPrefetchStrategy
|
58 |
|
59 | const preFetched = {}
|
60 |
|
61 | const prefetch = function(url) {
|
62 | return new Promise(resolve => {
|
63 | if (preFetched[url]) {
|
64 | resolve()
|
65 | return
|
66 | }
|
67 |
|
68 | supportedPrefetchStrategy(url)
|
69 | .then(() => {
|
70 | resolve()
|
71 | preFetched[url] = true
|
72 | })
|
73 | .catch(() => {})
|
74 | })
|
75 | }
|
76 |
|
77 | export default prefetch
|