Javscript weird logic behind

Javscript weird logic behind

I have tried some code in javascript and find out very weird/obscure logic
behind. Open chrome console for example and execute commads:
1) [] + []
2) [] +{}
3) {} + []
4) {} +{}
What you expect to see? I didn't expected something like that:
[] + []
answer: ""
[] +{}
answer: "[object Object]"
{} + []
answer: 0
{} +{}
answer: NaN
How javascript resolve those statements in such weird way?