Repository: tkh44/emotion (js)

Issue:
SSR + hyrdate causes two sets of <style> tags to be created
See example repo and follow the steps to install: https://github.com/zeit/next.js/tree/master/examples/with-emotion

- `emotion` version (same as that in the example repo, but also tried `6.0.3` and `7.0.4`)
- `react` version (`15.6.1` per the example repo)

What happened:

You can see below that there are two sets of `<style>` tags injected and it appears emotion is not respecting the IDs that were passed in with `hydrate`.

6.0.3:

![image](https://user-images.githubusercontent.com/626664/28800181-eaf58a6a-768e-11e7-8873-24acf1d2ce35.png)

7.0.4:

![image](https://user-images.githubusercontent.com/626664/28800259-40d211b0-768f-11e7-989c-f0601673f486.png)

I've also had this with my project using emotion but thought it would be easier to replicate by referring to the example repo.

Pull request:
Fix SSR hydration
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<!-- What changes are being made? (What feature/bug is being fixed here?) -->
**What**:

Fix SSR hydration for `keyframes`, `fontFace` and `injectGlobal`

I also added some tests for hydration to make sure styles don't get reinserted

Also, raw rules had hashes that were longer numbers so I changed the hashString export to call `.toString(36)` on the hash.

<!-- Why are these changes necessary? -->
**Why**:

Because otherwise rules get reinserted on the client.

<!-- How were these changes implemented? -->
**How**:

Don't filter out rules with the type `raw` or `keyframes` in `extractCritical`

<!-- Have you done all of these things?  -->
**Checklist**:
<!-- add "N/A" to the end of each line that's irrelevant to your changes -->
<!-- to check an item, place an "x" in the box like so: "- [x] Documentation" -->
- [ ] Documentation
- [ ] Tests
- [ ] Code complete

<!-- feel free to add additional comments -->

Closes #216 

I found an interesting problem while I was doing this which I'm not entirely sure how to solve.

Let's say you have a component which composes a class.

```jsx
const cls1 = css`
  color: hotpink;
`
const SomeComponent = styled.div`
  composes: ${cls1};
  background-color: yellow;
`
```

`cls1` won't be in the html so it won't be included in the `css` from `extractCritical` so it's inserted on the client.

Maybe we could solve this by inserting rules in `toString` so if they're not used as strings they're not inserted?

I'm not sure if this really matters that much since `insertRule` is so fast but in a large app with lots of `composes` lots of rules will be inserted that are never actually used.

@threepointone Would this also be a problem in glamor? if not how does glamor solve it?
```jsx
const cls1 = css({ color: 'hotpink' })
const classThatWillBeInHtml = css({ backgroundColor: 'yellow' }, cls1)
```


Patch:
diff --git a/src/hash.js b/src/hash.js
index b2fbbfad..7d00ac63 100644
--- a/src/hash.js
+++ b/src/hash.js
@@ -3,7 +3,7 @@
 
 export function hashArray (arr: string[]): string {
   let str = arr.join(',')
-  return hashString(str, str.length).toString(36)
+  return hashString(str)
 }
 
 export function hashObject (...objs: Array<{ [string]: any }>): string {
@@ -11,10 +11,14 @@ export function hashObject (...objs: Array<{ [string]: any }>): string {
   for (let i = 0; i < objs.length; i++) {
     str += JSON.stringify(objs[i])
   }
-  return hashString(str, str.length).toString(36)
+  return hashString(str)
 }
 
-export function hashString (str: string, seed: number) {
+export function hashString (str: string) {
+  return hash(str, str.length).toString(36)
+}
+
+function hash (str: string, seed: number) {
   let m = 0x5bd1e995
   let r = 24
   let h = seed ^ str.length
diff --git a/src/index.js b/src/index.js
index 937ba016..f647a2c1 100644
--- a/src/index.js
+++ b/src/index.js
@@ -77,7 +77,7 @@ export function css (objs: any, vars: Array<any>, content: () => Array<any>) {
 
 function insertRawRule (css: string) {
   let spec = {
-    id: hash(css, css.length),
+    id: hash(css),
     css,
     type: 'raw'
   }
diff --git a/src/server.js b/src/server.js
index 8d653b12..da3bfc7c 100644
--- a/src/server.js
+++ b/src/server.js
@@ -26,13 +26,18 @@ export function extractCritical (html) {
   }
 
   o.rules = sheet.sheet.cssRules.slice().filter(x => {
+    RGX.lastIndex = 0
     let match = RGX.exec(x.cssText)
     const ret = match == null || ids[match[1]] || false
-    RGX.lastIndex = 0
     return ret
   })
 
-  o.ids = keys(inserted).filter(id => !!ids[id])
+  o.ids = keys(inserted).filter(
+    id =>
+      !!ids[id] ||
+      sheet.registered[id].type === 'raw' ||
+      sheet.registered[id].type === 'keyframes'
+  )
 
   let css = ''
   forEach(o.rules, x => (css += x.cssText))


Test patch:
diff --git a/test/__snapshots__/server.test.js.snap b/test/__snapshots__/server.test.js.snap
index 0bd3ce14..aa81c4a9 100644
--- a/test/__snapshots__/server.test.js.snap
+++ b/test/__snapshots__/server.test.js.snap
@@ -2,21 +2,36 @@
 
 exports[`extractCritical returns static css 1`] = `
 Object {
-  "css": ".no-prefix {display:-webkit-box; display: -ms-flexbox; display: flex;-webkit-box-pack:center;-ms-flex-pack:center;justify-content:center;}.css-71uu79{display:-webkit-box; display: -ms-flexbox; display: flex;}.css-l2qi8{border-radius:50%;height:50px;width:50px;background-color:red;}",
-  "html": "<main class=\\"css-13bzyir0 css-71uu79\\" data-reactroot=\\"\\" data-reactid=\\"1\\" data-react-checksum=\\"452416722\\"><img size=\\"30\\" class=\\"css-13bzyir1 css-l2qi8\\" data-reactid=\\"2\\"/><img size=\\"100\\" class=\\"css-13bzyir1 css-l2qi8\\" data-reactid=\\"3\\"/><img class=\\"css-13bzyir1 css-l2qi8\\" data-reactid=\\"4\\"/></main>",
+  "css": "@font-face{font-family:'Patrick Hand SC';font-style:normal;font-weight:400;src:local('Patrick Hand SC'), local('PatrickHandSC-Regular'), url(https://fonts.gstatic.com/s/patrickhandsc/v4/OYFWCgfCR-7uHIovjUZXsZ71Uis0Qeb9Gqo8IZV7ckE.woff2) format('woff2');unicode-range:U+0100-024F, U+1E00-1EFF, U+20A0-20AB, U+20AD-20CF, U+2C60-2C7F, U+A720-A7FF;}@-webkit-keyframes animation_7jdctn{from, 20%, 53%, 80%, to {-webkit-animation-timing-function:cubic-bezier(0.215, 0.610, 0.355, 1.000);animation-timing-function:cubic-bezier(0.215, 0.610, 0.355, 1.000);-webkit-transform:translate3d(0,0,0);transform:translate3d(0,0,0);}40%, 43% {-webkit-animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);-webkit-transform:translate3d(0, -30px, 0);transform:translate3d(0, -30px, 0);}70% {-webkit-animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);-webkit-transform:translate3d(0, -15px, 0);transform:translate3d(0, -15px, 0);}90% {-webkit-transform:translate3d(0,-4px,0);transform:translate3d(0,-4px,0);}}@keyframes animation_7jdctn{from, 20%, 53%, 80%, to {-webkit-animation-timing-function:cubic-bezier(0.215, 0.610, 0.355, 1.000);animation-timing-function:cubic-bezier(0.215, 0.610, 0.355, 1.000);-webkit-transform:translate3d(0,0,0);transform:translate3d(0,0,0);}40%, 43% {-webkit-animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);-webkit-transform:translate3d(0, -30px, 0);transform:translate3d(0, -30px, 0);}70% {-webkit-animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);-webkit-transform:translate3d(0, -15px, 0);transform:translate3d(0, -15px, 0);}90% {-webkit-transform:translate3d(0,-4px,0);transform:translate3d(0,-4px,0);}}.no-prefix {display:-webkit-box; display: -ms-flexbox; display: flex;-webkit-box-pack:center;-ms-flex-pack:center;justify-content:center;}.css-1kjabrg{color:hotpink;display:-webkit-box; display: -ms-flexbox; display: flex;}.css-1kjabrg:hover{color:white;background-color:lightgray;border-color:aqua;-webkit-box-shadow:-15px -15px 0 0 aqua, -30px -30px 0 0 cornflowerblue;box-shadow:-15px -15px 0 0 aqua, -30px -30px 0 0 cornflowerblue;}.css-1j6ha19{-webkit-animation:animation_7jdctn;animation:animation_7jdctn;border-radius:50%;height:50px;width:50px;background-color:red;}",
+  "html": "<main class=\\"css-fcaqzd0 css-1kjabrg\\" data-reactroot=\\"\\" data-reactid=\\"1\\" data-react-checksum=\\"-997632446\\"><img size=\\"30\\" class=\\"css-fcaqzd1 css-1j6ha19\\" data-reactid=\\"2\\"/><img size=\\"100\\" class=\\"css-fcaqzd1 css-1j6ha19\\" data-reactid=\\"3\\"/><img class=\\"css-fcaqzd1 css-1j6ha19\\" data-reactid=\\"4\\"/></main>",
   "ids": Array [
-    "71uu79",
-    "l2qi8",
+    "1vx6krt",
+    "7jdctn",
+    "1tybtvv",
+    "1kjabrg",
+    "1j6ha19",
   ],
   "rules": Array [
+    Object {
+      "cssText": "@font-face{font-family:'Patrick Hand SC';font-style:normal;font-weight:400;src:local('Patrick Hand SC'), local('PatrickHandSC-Regular'), url(https://fonts.gstatic.com/s/patrickhandsc/v4/OYFWCgfCR-7uHIovjUZXsZ71Uis0Qeb9Gqo8IZV7ckE.woff2) format('woff2');unicode-range:U+0100-024F, U+1E00-1EFF, U+20A0-20AB, U+20AD-20CF, U+2C60-2C7F, U+A720-A7FF;}",
+    },
+    Object {
+      "cssText": "@-webkit-keyframes animation_7jdctn{from, 20%, 53%, 80%, to {-webkit-animation-timing-function:cubic-bezier(0.215, 0.610, 0.355, 1.000);animation-timing-function:cubic-bezier(0.215, 0.610, 0.355, 1.000);-webkit-transform:translate3d(0,0,0);transform:translate3d(0,0,0);}40%, 43% {-webkit-animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);-webkit-transform:translate3d(0, -30px, 0);transform:translate3d(0, -30px, 0);}70% {-webkit-animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);-webkit-transform:translate3d(0, -15px, 0);transform:translate3d(0, -15px, 0);}90% {-webkit-transform:translate3d(0,-4px,0);transform:translate3d(0,-4px,0);}}",
+    },
+    Object {
+      "cssText": "@keyframes animation_7jdctn{from, 20%, 53%, 80%, to {-webkit-animation-timing-function:cubic-bezier(0.215, 0.610, 0.355, 1.000);animation-timing-function:cubic-bezier(0.215, 0.610, 0.355, 1.000);-webkit-transform:translate3d(0,0,0);transform:translate3d(0,0,0);}40%, 43% {-webkit-animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);-webkit-transform:translate3d(0, -30px, 0);transform:translate3d(0, -30px, 0);}70% {-webkit-animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);-webkit-transform:translate3d(0, -15px, 0);transform:translate3d(0, -15px, 0);}90% {-webkit-transform:translate3d(0,-4px,0);transform:translate3d(0,-4px,0);}}",
+    },
     Object {
       "cssText": ".no-prefix {display:-webkit-box; display: -ms-flexbox; display: flex;-webkit-box-pack:center;-ms-flex-pack:center;justify-content:center;}",
     },
     Object {
-      "cssText": ".css-71uu79{display:-webkit-box; display: -ms-flexbox; display: flex;}",
+      "cssText": ".css-1kjabrg{color:hotpink;display:-webkit-box; display: -ms-flexbox; display: flex;}",
     },
     Object {
-      "cssText": ".css-l2qi8{border-radius:50%;height:50px;width:50px;background-color:red;}",
+      "cssText": ".css-1kjabrg:hover{color:white;background-color:lightgray;border-color:aqua;-webkit-box-shadow:-15px -15px 0 0 aqua, -30px -30px 0 0 cornflowerblue;box-shadow:-15px -15px 0 0 aqua, -30px -30px 0 0 cornflowerblue;}",
+    },
+    Object {
+      "cssText": ".css-1j6ha19{-webkit-animation:animation_7jdctn;animation:animation_7jdctn;border-radius:50%;height:50px;width:50px;background-color:red;}",
     },
   ],
 }
@@ -24,18 +39,84 @@ Object {
 
 exports[`extractCritical returns static css 2`] = `
 Object {
-  "css": ".no-prefix {display:-webkit-box; display: -ms-flexbox; display: flex;-webkit-box-pack:center;-ms-flex-pack:center;justify-content:center;}.css-71uu79{display:-webkit-box; display: -ms-flexbox; display: flex;}",
-  "html": "<main class=\\"css-13bzyir0 css-71uu79\\" data-reactroot=\\"\\" data-reactid=\\"1\\" data-react-checksum=\\"1740055930\\"><div data-reactid=\\"2\\">Hello</div></main>",
+  "css": "@font-face{font-family:'Patrick Hand SC';font-style:normal;font-weight:400;src:local('Patrick Hand SC'), local('PatrickHandSC-Regular'), url(https://fonts.gstatic.com/s/patrickhandsc/v4/OYFWCgfCR-7uHIovjUZXsZ71Uis0Qeb9Gqo8IZV7ckE.woff2) format('woff2');unicode-range:U+0100-024F, U+1E00-1EFF, U+20A0-20AB, U+20AD-20CF, U+2C60-2C7F, U+A720-A7FF;}@-webkit-keyframes animation_7jdctn{from, 20%, 53%, 80%, to {-webkit-animation-timing-function:cubic-bezier(0.215, 0.610, 0.355, 1.000);animation-timing-function:cubic-bezier(0.215, 0.610, 0.355, 1.000);-webkit-transform:translate3d(0,0,0);transform:translate3d(0,0,0);}40%, 43% {-webkit-animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);-webkit-transform:translate3d(0, -30px, 0);transform:translate3d(0, -30px, 0);}70% {-webkit-animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);-webkit-transform:translate3d(0, -15px, 0);transform:translate3d(0, -15px, 0);}90% {-webkit-transform:translate3d(0,-4px,0);transform:translate3d(0,-4px,0);}}@keyframes animation_7jdctn{from, 20%, 53%, 80%, to {-webkit-animation-timing-function:cubic-bezier(0.215, 0.610, 0.355, 1.000);animation-timing-function:cubic-bezier(0.215, 0.610, 0.355, 1.000);-webkit-transform:translate3d(0,0,0);transform:translate3d(0,0,0);}40%, 43% {-webkit-animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);-webkit-transform:translate3d(0, -30px, 0);transform:translate3d(0, -30px, 0);}70% {-webkit-animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);-webkit-transform:translate3d(0, -15px, 0);transform:translate3d(0, -15px, 0);}90% {-webkit-transform:translate3d(0,-4px,0);transform:translate3d(0,-4px,0);}}.no-prefix {display:-webkit-box; display: -ms-flexbox; display: flex;-webkit-box-pack:center;-ms-flex-pack:center;justify-content:center;}.css-1kjabrg{color:hotpink;display:-webkit-box; display: -ms-flexbox; display: flex;}.css-1kjabrg:hover{color:white;background-color:lightgray;border-color:aqua;-webkit-box-shadow:-15px -15px 0 0 aqua, -30px -30px 0 0 cornflowerblue;box-shadow:-15px -15px 0 0 aqua, -30px -30px 0 0 cornflowerblue;}",
+  "html": "<main class=\\"css-fcaqzd0 css-1kjabrg\\" data-reactroot=\\"\\" data-reactid=\\"1\\" data-react-checksum=\\"-1456331201\\"><div data-reactid=\\"2\\">Hello</div></main>",
   "ids": Array [
-    "71uu79",
+    "1vx6krt",
+    "7jdctn",
+    "1tybtvv",
+    "1kjabrg",
   ],
   "rules": Array [
+    Object {
+      "cssText": "@font-face{font-family:'Patrick Hand SC';font-style:normal;font-weight:400;src:local('Patrick Hand SC'), local('PatrickHandSC-Regular'), url(https://fonts.gstatic.com/s/patrickhandsc/v4/OYFWCgfCR-7uHIovjUZXsZ71Uis0Qeb9Gqo8IZV7ckE.woff2) format('woff2');unicode-range:U+0100-024F, U+1E00-1EFF, U+20A0-20AB, U+20AD-20CF, U+2C60-2C7F, U+A720-A7FF;}",
+    },
+    Object {
+      "cssText": "@-webkit-keyframes animation_7jdctn{from, 20%, 53%, 80%, to {-webkit-animation-timing-function:cubic-bezier(0.215, 0.610, 0.355, 1.000);animation-timing-function:cubic-bezier(0.215, 0.610, 0.355, 1.000);-webkit-transform:translate3d(0,0,0);transform:translate3d(0,0,0);}40%, 43% {-webkit-animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);-webkit-transform:translate3d(0, -30px, 0);transform:translate3d(0, -30px, 0);}70% {-webkit-animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);-webkit-transform:translate3d(0, -15px, 0);transform:translate3d(0, -15px, 0);}90% {-webkit-transform:translate3d(0,-4px,0);transform:translate3d(0,-4px,0);}}",
+    },
+    Object {
+      "cssText": "@keyframes animation_7jdctn{from, 20%, 53%, 80%, to {-webkit-animation-timing-function:cubic-bezier(0.215, 0.610, 0.355, 1.000);animation-timing-function:cubic-bezier(0.215, 0.610, 0.355, 1.000);-webkit-transform:translate3d(0,0,0);transform:translate3d(0,0,0);}40%, 43% {-webkit-animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);-webkit-transform:translate3d(0, -30px, 0);transform:translate3d(0, -30px, 0);}70% {-webkit-animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);-webkit-transform:translate3d(0, -15px, 0);transform:translate3d(0, -15px, 0);}90% {-webkit-transform:translate3d(0,-4px,0);transform:translate3d(0,-4px,0);}}",
+    },
     Object {
       "cssText": ".no-prefix {display:-webkit-box; display: -ms-flexbox; display: flex;-webkit-box-pack:center;-ms-flex-pack:center;justify-content:center;}",
     },
     Object {
-      "cssText": ".css-71uu79{display:-webkit-box; display: -ms-flexbox; display: flex;}",
+      "cssText": ".css-1kjabrg{color:hotpink;display:-webkit-box; display: -ms-flexbox; display: flex;}",
+    },
+    Object {
+      "cssText": ".css-1kjabrg:hover{color:white;background-color:lightgray;border-color:aqua;-webkit-box-shadow:-15px -15px 0 0 aqua, -30px -30px 0 0 cornflowerblue;box-shadow:-15px -15px 0 0 aqua, -30px -30px 0 0 cornflowerblue;}",
     },
   ],
 }
 `;
+
+exports[`hydration only rules that are not in the critical css are inserted 1`] = `
+Object {
+  "css": "@font-face{font-family:'Patrick Hand SC';font-style:normal;font-weight:400;src:local('Patrick Hand SC'), local('PatrickHandSC-Regular'), url(https://fonts.gstatic.com/s/patrickhandsc/v4/OYFWCgfCR-7uHIovjUZXsZ71Uis0Qeb9Gqo8IZV7ckE.woff2) format('woff2');unicode-range:U+0100-024F, U+1E00-1EFF, U+20A0-20AB, U+20AD-20CF, U+2C60-2C7F, U+A720-A7FF;}@-webkit-keyframes animation_7jdctn{from, 20%, 53%, 80%, to {-webkit-animation-timing-function:cubic-bezier(0.215, 0.610, 0.355, 1.000);animation-timing-function:cubic-bezier(0.215, 0.610, 0.355, 1.000);-webkit-transform:translate3d(0,0,0);transform:translate3d(0,0,0);}40%, 43% {-webkit-animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);-webkit-transform:translate3d(0, -30px, 0);transform:translate3d(0, -30px, 0);}70% {-webkit-animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);-webkit-transform:translate3d(0, -15px, 0);transform:translate3d(0, -15px, 0);}90% {-webkit-transform:translate3d(0,-4px,0);transform:translate3d(0,-4px,0);}}@keyframes animation_7jdctn{from, 20%, 53%, 80%, to {-webkit-animation-timing-function:cubic-bezier(0.215, 0.610, 0.355, 1.000);animation-timing-function:cubic-bezier(0.215, 0.610, 0.355, 1.000);-webkit-transform:translate3d(0,0,0);transform:translate3d(0,0,0);}40%, 43% {-webkit-animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);-webkit-transform:translate3d(0, -30px, 0);transform:translate3d(0, -30px, 0);}70% {-webkit-animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);-webkit-transform:translate3d(0, -15px, 0);transform:translate3d(0, -15px, 0);}90% {-webkit-transform:translate3d(0,-4px,0);transform:translate3d(0,-4px,0);}}.no-prefix {display:-webkit-box; display: -ms-flexbox; display: flex;-webkit-box-pack:center;-ms-flex-pack:center;justify-content:center;}.css-1kjabrg{color:hotpink;display:-webkit-box; display: -ms-flexbox; display: flex;}.css-1kjabrg:hover{color:white;background-color:lightgray;border-color:aqua;-webkit-box-shadow:-15px -15px 0 0 aqua, -30px -30px 0 0 cornflowerblue;box-shadow:-15px -15px 0 0 aqua, -30px -30px 0 0 cornflowerblue;}.css-1j6ha19{-webkit-animation:animation_7jdctn;animation:animation_7jdctn;border-radius:50%;height:50px;width:50px;background-color:red;}",
+  "html": "<main class=\\"css-fcaqzd0 css-1kjabrg\\" data-reactroot=\\"\\" data-reactid=\\"1\\" data-react-checksum=\\"-997632446\\"><img size=\\"30\\" class=\\"css-fcaqzd1 css-1j6ha19\\" data-reactid=\\"2\\"/><img size=\\"100\\" class=\\"css-fcaqzd1 css-1j6ha19\\" data-reactid=\\"3\\"/><img class=\\"css-fcaqzd1 css-1j6ha19\\" data-reactid=\\"4\\"/></main>",
+  "ids": Array [
+    "1vx6krt",
+    "7jdctn",
+    "1tybtvv",
+    "1kjabrg",
+    "1j6ha19",
+  ],
+  "rules": Array [
+    Object {
+      "cssText": "@font-face{font-family:'Patrick Hand SC';font-style:normal;font-weight:400;src:local('Patrick Hand SC'), local('PatrickHandSC-Regular'), url(https://fonts.gstatic.com/s/patrickhandsc/v4/OYFWCgfCR-7uHIovjUZXsZ71Uis0Qeb9Gqo8IZV7ckE.woff2) format('woff2');unicode-range:U+0100-024F, U+1E00-1EFF, U+20A0-20AB, U+20AD-20CF, U+2C60-2C7F, U+A720-A7FF;}",
+    },
+    Object {
+      "cssText": "@-webkit-keyframes animation_7jdctn{from, 20%, 53%, 80%, to {-webkit-animation-timing-function:cubic-bezier(0.215, 0.610, 0.355, 1.000);animation-timing-function:cubic-bezier(0.215, 0.610, 0.355, 1.000);-webkit-transform:translate3d(0,0,0);transform:translate3d(0,0,0);}40%, 43% {-webkit-animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);-webkit-transform:translate3d(0, -30px, 0);transform:translate3d(0, -30px, 0);}70% {-webkit-animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);-webkit-transform:translate3d(0, -15px, 0);transform:translate3d(0, -15px, 0);}90% {-webkit-transform:translate3d(0,-4px,0);transform:translate3d(0,-4px,0);}}",
+    },
+    Object {
+      "cssText": "@keyframes animation_7jdctn{from, 20%, 53%, 80%, to {-webkit-animation-timing-function:cubic-bezier(0.215, 0.610, 0.355, 1.000);animation-timing-function:cubic-bezier(0.215, 0.610, 0.355, 1.000);-webkit-transform:translate3d(0,0,0);transform:translate3d(0,0,0);}40%, 43% {-webkit-animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);-webkit-transform:translate3d(0, -30px, 0);transform:translate3d(0, -30px, 0);}70% {-webkit-animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);animation-timing-function:cubic-bezier(0.755, 0.050, 0.855, 0.060);-webkit-transform:translate3d(0, -15px, 0);transform:translate3d(0, -15px, 0);}90% {-webkit-transform:translate3d(0,-4px,0);transform:translate3d(0,-4px,0);}}",
+    },
+    Object {
+      "cssText": ".no-prefix {display:-webkit-box; display: -ms-flexbox; display: flex;-webkit-box-pack:center;-ms-flex-pack:center;justify-content:center;}",
+    },
+    Object {
+      "cssText": ".css-1kjabrg{color:hotpink;display:-webkit-box; display: -ms-flexbox; display: flex;}",
+    },
+    Object {
+      "cssText": ".css-1kjabrg:hover{color:white;background-color:lightgray;border-color:aqua;-webkit-box-shadow:-15px -15px 0 0 aqua, -30px -30px 0 0 cornflowerblue;box-shadow:-15px -15px 0 0 aqua, -30px -30px 0 0 cornflowerblue;}",
+    },
+    Object {
+      "cssText": ".css-1j6ha19{-webkit-animation:animation_7jdctn;animation:animation_7jdctn;border-radius:50%;height:50px;width:50px;background-color:red;}",
+    },
+  ],
+}
+`;
+
+exports[`hydration only rules that are not in the critical css are inserted 2`] = `
+Array [
+  Object {
+    "cssText": ".css-hjkr8p{color:hotpink;}",
+  },
+  Object {
+    "cssText": ".css-hjkr8p:hover{color:white;background-color:lightgray;border-color:aqua;-webkit-box-shadow:-15px -15px 0 0 aqua, -30px -30px 0 0 cornflowerblue;box-shadow:-15px -15px 0 0 aqua, -30px -30px 0 0 cornflowerblue;}",
+  },
+  Object {
+    "cssText": ".css-trriyv{display:none;name:unused-class;}",
+  },
+]
+`;
diff --git a/test/server.test.js b/test/server.test.js
index 7b193996..ca043fcb 100644
--- a/test/server.test.js
+++ b/test/server.test.js
@@ -5,50 +5,109 @@
 import React from 'react'
 import { renderToString } from 'react-dom/server'
 import styled from '../src/react'
-import { css, injectGlobal } from '../src/index'
+import { css, injectGlobal, keyframes, flush, hydrate, fontFace, sheet } from '../src/index'
 import { extractCritical } from '../src/server'
 
-const color = 'red'
+const getComponents = () => {
+  const color = 'red'
 
-const Main = styled.main`display: flex;`
+  fontFace`
+    font-family: 'Patrick Hand SC';
+    font-style: normal;
+    font-weight: 400;
+    src: local('Patrick Hand SC'), local('PatrickHandSC-Regular'), url(https://fonts.gstatic.com/s/patrickhandsc/v4/OYFWCgfCR-7uHIovjUZXsZ71Uis0Qeb9Gqo8IZV7ckE.woff2) format('woff2');
+    unicode-range: U+0100-024F, U+1E00-1EFF, U+20A0-20AB, U+20AD-20CF, U+2C60-2C7F, U+A720-A7FF;
+  `
 
-const Image = styled.img`
-  border-radius: 50%;
-  height: 50px;
-  width: 50px;
-  background-color: ${color};
-`
+  const bounce = keyframes`
+    from, 20%, 53%, 80%, to {
+      animation-timing-function: cubic-bezier(0.215, 0.610, 0.355, 1.000);
+      transform: translate3d(0,0,0);
+    }
 
-// this will not be included since it's not used
-css`
-  display: none;
-  name: unused-class;
-`
+    40%, 43% {
+      animation-timing-function: cubic-bezier(0.755, 0.050, 0.855, 0.060);
+      transform: translate3d(0, -30px, 0);
+    }
 
-// this will be included in both because it doesn't have the css- prefix
+    70% {
+      animation-timing-function: cubic-bezier(0.755, 0.050, 0.855, 0.060);
+      transform: translate3d(0, -15px, 0);
+    }
 
-injectGlobal`
-  .no-prefix {
+    90% {
+      transform: translate3d(0,-4px,0);
+    }
+  `
+
+  const hoverStyles = css`
+    color: hotpink;
+    &:hover {
+      color: white;
+      background-color: lightgray;
+      border-color: aqua;
+      box-shadow: -15px -15px 0 0 aqua, -30px -30px 0 0 cornflowerblue;
+    }
+  `
+
+  const Main = styled.main`
+    composes: ${hoverStyles};
     display: flex;
-    justify-content: center;
-  }
-`
-
-const Page1 = () =>
-  <Main>
-    <Image size={30} />
-    <Image size={100} />
-    <Image />
-  </Main>
-
-const Page2 = () =>
-  <Main>
-    <div>Hello</div>
-  </Main>
+  `
+
+  const Image = styled.img`
+    animation: ${bounce};
+    border-radius: 50%;
+    height: 50px;
+    width: 50px;
+    background-color: ${color};
+  `
+
+  // this will not be included since it's not used
+  css`
+    display: none;
+    name: unused-class;
+  `
+
+  // this will be included in both because it doesn't have the css- prefix
+
+  injectGlobal`
+    .no-prefix {
+      display: flex;
+      justify-content: center;
+    }
+  `
+
+  const Page1 = () =>
+    <Main>
+      <Image size={30} />
+      <Image size={100} />
+      <Image />
+    </Main>
+
+  const Page2 = () =>
+    <Main>
+      <div>Hello</div>
+    </Main>
+  return { Page1, Page2 }
+}
 
 describe('extractCritical', () => {
   test('returns static css', () => {
+    const { Page1, Page2 } = getComponents()
     expect(extractCritical(renderToString(<Page1 />))).toMatchSnapshot()
     expect(extractCritical(renderToString(<Page2 />))).toMatchSnapshot()
   })
 })
+describe('hydration', () => {
+  test('only rules that are not in the critical css are inserted', () => {
+    const { Page1 } = getComponents()
+    const { html, ids, css, rules } = extractCritical(renderToString(<Page1 />))
+    expect({ html, ids, css, rules }).toMatchSnapshot()
+    flush()
+    hydrate(ids)
+    const { Page1: NewPage1 } = getComponents()
+    renderToString(<NewPage1 />)
+    expect(sheet.sheet.cssRules).toMatchSnapshot()
+  })
+})