Bootstrap 4 drops support for Internet Explorer 8 and 9, but you can add it back by simply adding a conditional statement targeting IE 8 and 9 with a CSS file and a CDN-hosted JavaScript file to polyfill HTML5 element support.

1. Add <meta http-equiv="x-ua-compatible" content="ie=edge"> to the top of the of your page

2. Add the following conditional statements to the of your page but after the Bootstrap 4 CSS:

    <!--[if IE]>
      <link href="https://cdn.jsdelivr.net/gh/coliff/bootstrap-ie8/css/bootstrap-ie9.min.css" rel="stylesheet">
      <script src="https://cdn.jsdelivr.net/g/[email protected]"></script>
    <![endif]-->
    <!--[if lt IE 9]>
	  <link href="https://cdn.jsdelivr.net/gh/coliff/bootstrap-ie8/css/bootstrap-ie8.min.css" rel="stylesheet">
    <![endif]-->

Q. What does this fix/polyfill?

A. Internet Explorer 9 doesn't support flexbox so there is a float-based layout fallback and a couple of other minor fixes. Internet Explorer 8 doesn't support rem units so all units are specified in pixels. Media Queries are also not supported so IE8 has a fixed-width layout (min-width 998px).

Q. What about IE7?

A. This doesn't include any IE7-specific fixes, but it should make it look more presentable.

Q. Is the CSS hosted on a CDN?

A. Yes, thanks to JSDelivr minified versions are available with the direct links:

https://cdn.jsdelivr.net/gh/coliff/bootstrap-ie8/css/bootstrap-ie8.min.css

https://cdn.jsdelivr.net/gh/coliff/bootstrap-ie8/css/bootstrap-ie9.min.css

Q. Why is the JavaScript completely broken on IE8?

A. jQuery 3.x doesn't work with IE8 at all - you'll need to load jQuery 1.x. You can do this using conditional comments if you like - see this gist.

Q. Will you provide LESS/SASS files?

A. Maybe in a future release I'll provide SASS file (with comments).

Q. Do I need the RespondJS polyfill for IE8 like Bootstrap 3 uses?

A. No. Instead the CSS is set to be fixed-width which makes things a lot easier. You don't need to change your HTML markup, the CSS will take care of it as the (min-width:992px) media queries are all set.

Q. Where can I see a demo?

A. Right here: https://coliff.github.io/bootstrap-ie8/test.htm

• As this is only a CSS stylesheet there are problems with using Bootstrap 4's JavaScript in IE8. An easy workaround is to include a link to the Bootstrap v3 JS file (this fixes the dropdown menus) within the conditional statement. Be sure to use jQuery 1.x too.
• View a list of known issues at https://github.com/coliff/bootstrap-ie8/issues