How do I change the content of a DOM element?
Use:
innerHTML
This will take the string you pass in and interpret it as HTML.
innerText
This will not interpret the string you pass in - it will treat any HTML markup as plain text and not try to treat it as HTML.
For example:
var Div = document.querySelector(".SPLASHdiv");
Div.innerHTML = "This is <b>good!</b>";
This is a core technique in Javascript web programming.
See this video to see it in use.