Question

If I have

a = 0;
if(a++ < 1){
    console.log(a);
}

I get the value 1 in the console. If a became 1 with the incrementation, then why did the expression evaluate true?

If I do

a = 0;
if(++a < 1){
    console.log(a);
}

Then I don’t get anything in the console, meaning the expression evaluated to be false.

I have always used variable++ to increment variables in for loops and the like. I have seen the ++variable, but I assumed it was another way to write the same thing. Can someone explain what happens and why? What’s the difference between the two?

Does ++variable increment the variable at the time of evaluation, while variable++ increments after?

Answer 1

I have seen the ++variable, but I assumed it was another way to write the same thing.

No, they’re not the same at all.

• ++variable is pre-increment.
  It increments variable and evaluates to the new value.

• variable++ is post-increment.
  It increments variable and evaluates to the old value.

This is common to most C-style languages, including C itself, C++, PHP, Java and Javascript.

i.e.:

Does ++variable increment the variable at the time of evaluation, while variable++ increments after?

Yes, exactly. 🙂