What I learned making my website compatible with Internet Explorer 5


Accessibility CSS HTML Javascript

When I opened my website with Internet Explorer 5, it was just good enough that I thought "Hey, I can work with this." I think it might be helpful for somebody if I wrote about what I found. Here are some of the weird and surprising things I learned making my website work in Internet Explorer 5.


Side note: There are Javascript transpilers that can usually turn ES6 features into something to as early as ES3. I use Typescript to do this in other projects, but configuring and managing it would be overkill for the 2kb of JS on this website.

Moderately weird IE things

1. CSS Variables/Custom Properties (IE 11 and below)

I discovered that SCSS variables and functions are your friend when it comes to supporting IE. They compile down to vanilla CSS, which is fantastic.

That's great, but sometimes we need a variable to change at runtime, when somebody interacts with the site. SCSS variables (which compile to static values), can't do that. That's okay! In Internet Explorer, CSS custom properties are treated the same as any other invalid property value, so it doesn't hurt anything to use them, as long as you provide a static value as a fallback.

$primary: red;

body {
    --primary: #{$primary};

body.dark_mode {
    --primary: blue; /* color will change for users with modern browsers */

button {
    color: $primary; /* fallback value if no custom property support */
    color: var(--primary);

2. Wave goodbye to (most) CSS relative units 👋 (IE 8 and below)

Enjoy using relative units like rem, vw, vh, vmin, vmax? Forget about it. You'll become well acquainted with % and px and font-size: small. This was annoying at first, because I use rem all over my stylesheets. My solution was to load in a separate stylesheet for 'retro' users, and make a small SCSS function that could convert rem-size numbers to pixels for me.

@function rem($n) {
    @return ($n * 20) + px;

h1 {
    font-size: rem(4); /* 80px */

Very weird IE things

3. Type Mismatch Error (IE 9 and below)

type mismatch error in the console

This is probably the most mysterious and elusive error I've encountered while coding. Googling didn't help, and I ended up just trying different methods or APIs until it went away. Let me know if you have some insight on this one - for real.

4. HTML5 semantic elements aren't semantic?! (IE 8 and below)

I try to be a responsible developer, so I use semantic elements like nav, article, and footer. I was confused to find that content inside these elements gets unwrapped by Internet Explorer. IE goes looking for the next valid parent up the DOM tree and puts your content there instead.

<!-- this -->

    © 2020 Dev-Signers, Inc.

<!-- becomes this -->

© 2020 Dev-Signers, Inc.

Here's a list of HTML5 elements that won't work in Internet Explorer. See caniuse.com for details.

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