Postfix increment (i.e. n++) is usually explained as such:
- Tell me the value of n
- Increment the value of n
And prefix increment (++n):
- Increment the value of n
- Tell me the value of n
That is practically correct; however, it is not technically correct. At least not in javascript.
According to the spec, the prefix increment (after being translated into a more humane form and disregarding strict-mode regulations), is this:
- Save the numerical value of n to T0
- Increment the value of T0 (without changing it)
- Store that new value in n
- Tell me the value of n
And postfix increment:
- Save the numerical value of n to T0
- Increment the value of T0 (without changing it)
- Store that new value in n
- Tell me the value of T0
So, what's the difference between the practical explanation and the technical one? The main difference is the timeline. In the practical explanation, the increment happens at different times. Technically, it happens in the exact same time - the only difference is which value is being returned.
You may now carry on with your life.
Kicking myself for not wondering why the typical explanation doesn't explain parens failing to force eval as you would expect. The practical explanation doesn't really cover this:
var x=2, y=(x++); //y still equals 2 and now I finally freaking know why. x is never returned in x++