I have to explain double backslash bit at 9:07.

TL;DR

Don't do : bits in HTML's attributes, there's data- attributes specifically for that reason, which could be easily fetched through dataset among other things (MDN Link).

Longer Explanation

The : has special meaning in CSS selectors, you need to escape it with a \ character. And since you need the \ to get passed through as part of the selector, you need to escape it in your JavaScript.

The successful call therefore looks like:

document.querySelector('[wire\\\:myattribute="value"]');

Storing a Snapshot