When to use Vanilla JavaScript vs. jQuery?

Question

I have noticed while monitoring/attempting to answer common jQuery questions, that there are certain practices using javascript, instead of jQuery, that actually enable you

Answer 1

When:

1. you know that there is unflinching cross-browser support for what you are doing, and
2. it is not significantly more code to type, and
3. it is not significantly less readable, and
4. you are reasonably confident that jQuery will not choose different implementations based on the browser to achieve better performance, then:

use JavaScript. Otherwise use jQuery (if you can).

Edit: This answer applies both when choosing to use jQuery overall versus leaving it out, as well as choosing whether to to use vanilla JS inside jQuery. Choosing between attr('id') and .id leans in favor of JS, while choosing between removeClass('foo') versus .className = .className.replace( new Regexp("(?:^|\\s+)"+foo+"(?:\\s+|$)",'g'), '' ) leans in favor of jQuery.