KA Hearth

A small blog where Matthias posted thoughts on things happening around Khan Academy. (Archived) About Me

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Using ES6 in KA HTML


Using ES6 in the KA webpage environment is obviously desirable. And unlike the Processing.JS environment, it’s quite feasible.

For detail on how and why KA parses your HTML, see this post, which seeks to answer how to disable Slowparse for large swaths of HTML.

The trick

If, however, you merely want to disable KA’s parsing of your Javascript, you can put your Javascript inside a script tag with the type set to application/javascript.

Unfortunately, because KA doesn’t completely clear the window before re-running code, you can’t use const or let.

This technique also has the benefit/risk of bypassing KA’s infinite loop protection.

How it works

Slowparse tries to follow the HTML spec as closely as possible, so it ignores script blocks that don’t have a script type set to text/javascript (or unset of course). Browsers, on the other hand, will run code with a script that is any of the valid MIME types (or unset, or an empty string).


<!DOCTYPE html>
    <meta charset="utf-8">
    <script type="application/javascript">
        // `var` because `let` and `const` still don't work  
        var test = () => {