Repository: create-react-app
Issue: Fonts are not loaded in IE11 with built app
Labels: issue: needs investigation

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### Is this a bug report?

Yes

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Yes 

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_fonts_


### Environment

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> Environment:
>   OS:  macOS High Sierra 10.13.4
>   Node:  8.9.4
>   Yarn:  1.6.0
>   npm:  5.6.0
>   Watchman:  Not Found
>   Xcode:  Not Found
>   Android Studio:  Not Found
> 
> Packages: (wanted => installed)
>   react: ^16.4.0 => 16.4.0
>   react-dom: ^16.4.0 => 16.4.0
>   react-scripts: 1.1.4 => 1.1.4

### Steps to Reproduce

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1. Create a new project with `create-react-app`
2. Add a font in the `src/font` dir
3. Add the necessary CSS to use this font using `@font-face` in `index.css` like in this example:

```css
@font-face {
    font-family: 'OpenSans-Regular';
    src: url('./fonts/OpenSans/OpenSans-Regular-webfont.eot?#iefix') format('embedded-opentype'),
         url('./fonts/OpenSans/OpenSans-Regular-webfont.woff') format('woff');
    font-weight: normal;
    font-style: normal;
}

body {
  margin: 0;
  padding: 0;
  font-family: 'OpenSans-Regular', sans-serif;
}
```

4. Run `yarn start` and open http://localhost:3000 in Internet Explorer 11 (using a VM may be a nice idea) and check that your font is used for the text (this is the expected behavior).
5. Stop the process and run `yarn build`
6. Run the built page by running `serve -s build`
7. Open http://localhost:3000 with Chrome, Firefox, etc. You will see that the used font is OpenSans
8. Now open the same URL with Internet Explorer 11.


### Expected Behavior

IE11 should display the text with the OpenSans font when the project is built.
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### Actual Behavior

The OpenSans font is not downloaded and the text is shown as sans-serif.
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**IE 11 (see how the text is rendered):**

![ie](https://user-images.githubusercontent.com/344445/41108270-68076602-6a74-11e8-8a40-000759844ddc.png)

**Chrome:**
<img width="1000" alt="react_app_-_font_test" src="https://user-images.githubusercontent.com/344445/41108272-6ad63868-6a74-11e8-90dd-5f43abdfa026.png">



### Reproducible Demo

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I created a repository to show the problem here: https://github.com/michaelperrin/create-react-app-font-problem.
Steps to reproduce:

1. Clone my demo repo: `git clone https://github.com/michaelperrin/create-react-app-font-problem.git`
2. Run the following commands:

```
 yarn global add serve
 yarn build
 serve -s build
```

3. Open http://localhost:3000 with Chrome, Firefox, etc. You will see that the used font is OpenSans
4. Now open the same URL with Internet Explorer 11 (using a VM may be a nice idea).


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**A few notes:**

* This is not due to the fact that you are running the project on localhost (I hosted it on a server and got the same problem).
* This is not due to font formats (IE11 does support EOT files).
* This happens with any font.
* This is not due to security parameters of IE11 (font download is enabled).
* I hope I didn't miss something and that this is an actual bug 😉