getElementById usage?

[drhuffman12]

How do I do something like (https://www.w3schools.com/jsref/met_document_getelementbyid.asp):

const myElement = document.getElementById("demo");
myElement.style.color = "red";

I tried some variations, none which worked:

# src/main.cr
...
require "web"
# require "js"

window = Web.window
console = window.console
document = window.document

# variants, not working:
demo = document.get_Element_By_Id("demo")
demo = document.get_element_by_id("demo")
demo = document.elementById("demo")
demo = document.element_by_id("demo")
demo = document.getelementbyid("demo")

These all gave errors like: Error: undefined method 'elementById' for Web::HTMLDocument when I run lib/js/scripts/build.sh src/main.cr

For that matter, how do I convert the JS style naming to Crystal style naming? Or, how do I get a list of methods for an object?