$0 is a reference to the currently selected html node in the Elements pane.
$1 is the one selected previously,
$2 the one before that, etc. up to the number
You can use that additional references to try out some relative operations
$ in the console is an alias for the lengthy
That’s if you don’t already have
$ variable defined in your app (e.g. jQuery)
$$ is an even bigger timesaver, because it not only runs document.QuerySelectorAll but also returns an array of nodes instead of NodeList type.
Array.from(document.querySelectorAll('div')) === $$('div')
$_ variable references the result of the last evaluated expression.
With the Console Importer browser extension for Chrome you can quickly import and play with npm libraries right in the console.
Just run e.g.
$i('moment') and after a couple of seconds you have lodash / momentjs available.