Inconsistency with `indexOf`

[KTibow]

htmx does operations with strings throughout it. However, it's not very consistent.

Since htmx has to work in IE11, it can't use .startsWith, so it has a startsWith function. However, there are a couple odd things:

• the logic isn't as simple as str.indexOf(prefix) === 0, instead it does some more logic with substring
• in some places, str.indexOf(prefix) === 0 is used instead of calling startsWith

[andryyy]

From the main page. 🙂