What's the meaning of the numbers printed below the message of console.log?

Question

I'm doing some testing in chrome debugger tool, I find some strange numbers are printed below the texts output by console.log:

I didn't log in the console, why are they there? what are these numbers? what does it mean?

Answer 1

The Chrome console logs the value of the last expression executed. In the first example above, the last line, i++; logs 9. In the second example, i+=1; logs 10.