Correct URI Encoding Order

packages/next/client/page-loader.js

@@ -15,7 +15,7 @@ function preloadScript(url) {
   const link = document.createElement('link')
   link.rel = 'preload'
   link.crossOrigin = process.crossOrigin
-  link.href = encodeURI(url)
+  link.href = url
   link.as = 'script'
   document.head.appendChild(link)
 }
@@ -44,7 +44,8 @@ export default class PageLoader {
   // Returns a promise for the dependencies for a particular route
   getDependencies(route) {
     return this.promisedBuildManifest.then(
-      man => (man[route] && man[route].map(url => `/_next/${url}`)) || []
+      man =>
+        (man[route] && man[route].map(url => `/_next/${encodeURI(url)}`)) || []
     )
   }
 
@@ -122,7 +123,7 @@ export default class PageLoader {
 
     const url = `${this.assetPrefix}/_next/static/${encodeURIComponent(
       this.buildId
-    )}/pages${scriptRoute}`
+    )}/pages${encodeURI(scriptRoute)}`
     this.loadScript(url, route, true)
   }
 
@@ -135,7 +136,7 @@ export default class PageLoader {
       if (isPage) url = url.replace(/\.js$/, '.module.js')
     }
     script.crossOrigin = process.crossOrigin
-    script.src = encodeURI(url)
+    script.src = url
     script.onerror = () => {
       const error = new Error(`Error loading script ${url}`)
       error.code = 'PAGE_LOAD_ERROR'
@@ -194,9 +195,9 @@ export default class PageLoader {
       this.assetPrefix +
       (isDependency
         ? route
-        : `/_next/static/${encodeURIComponent(
-            this.buildId
-          )}/pages${scriptRoute}`)
+        : `/_next/static/${encodeURIComponent(this.buildId)}/pages${encodeURI(
+            scriptRoute
+          )}`)
 
     // n.b. If preload is not supported, we fall back to `loadPage` which has
     // its own deduping mechanism.

test/integration/preload-viewport/pages/dynamic/[hello].js

@@ -0,0 +1 @@
+export default () => <p>Hello world</p>

test/integration/preload-viewport/pages/multi-prefetch.js

@@ -0,0 +1,19 @@
+import Link from 'next/link'
+import { useEffect } from 'react'
+import { useRouter } from 'next/router'
+
+export default () => {
+  const router = useRouter()
+  useEffect(() => {
+    router.prefetch('/dynamic/[hello]')
+    router.prefetch('/dynamic/[hello]')
+    router.prefetch('/dynamic/[hello]')
+  }, [router])
+  return (
+    <div>
+      <Link prefetch={true} href="/dynamic/[hello]" as={'/dynamic/test'}>
+        <a>I should only be prefetched once</a>
+      </Link>
+    </div>
+  )
+}

test/integration/preload-viewport/test/index.test.js

@@ -138,4 +138,24 @@ describe('Prefetching Links in viewport', () => {
     }
     expect(found).toBe(false)
   })
+
+  it('should not duplicate prefetches', async () => {
+    const browser = await webdriver(appPort, '/multi-prefetch')
+    await waitFor(2 * 1000)
+
+    const links = await browser.elementsByCss('link[rel=preload]')
+
+    const hrefs = []
+    for (const link of links) {
+      const href = await link.getAttribute('href')
+      hrefs.push(href)
+    }
+    hrefs.sort()
+
+    // Ensure no duplicates
+    expect(hrefs).toEqual([...new Set(hrefs)])
+
+    // Verify encoding
+    expect(hrefs.some(e => e.includes(`%5Bhello%5D.js`))).toBe(true)
+  })
 })