What does this log?

The + operator first turns objects into primitive values (simple values like strings and numbers). If either side is then a string, + joins the two as strings.
• [] becomes '' and {} becomes '[object Object]', so [] + {} is '[object Object]'.
• '5' + 2 joins strings and gives '52'.
• The - operator only works on numbers, so '5' - 2 turns '5' into 5 and gives 3.
• true + 1 turns true into 1 and gives 2.

The tempting option "0 3 7 2" is wrong because + with a string joins text. It does not add numbers.