Why Javascript acts like this? [duplicate]

Question

If I do:

var a = 1;
console.log(a) // 1
console.log(++a) // 2
console.log(a++) // 2
console.log(a) // 3

So to try make sense of this I would say:

Assign 1 to var a.
a now is 1. So it prints 1.
Now, INSIDE function console.log I sum to a 1. So it should print 2. The sum happens BEFORE printing the value.
Why the value 1 is added to a AFTER printing the actual value of a? This is what I don't get.

How JavaScript works so that this can happen?

is nothing unexpected, ++a is added before which is 2 from 1, a++ is added after so its still 2, then last is outputting 3 because it was added in prev line — Lawrence Cherone
– Lawrence Cherone, Commented Sep 30, 2020 at 20:32
Do you know the difference between pre-increment and post-increment? You may need to look more closely here. These have a different behaviour for a reason. — tadman
– tadman, Commented Sep 30, 2020 at 20:33
in number 3, when you say "I sum to a", you should instead say "I pre-increment a". — jarmod
– jarmod, Commented Sep 30, 2020 at 20:34
Didn't know that a console.log() could execute instead of just printing the variable — Warface
– Warface, Commented Sep 30, 2020 at 23:04

abney317 · Accepted Answer · 2025-04-12 05:09:19Z

3

This is the difference between a pre-increment and post-increment.

++a will add 1 before the final value is evaluated.

a++ will evaluate a and then add 1 afterwards.

edited Apr 12 at 5:09

answered Sep 30, 2020 at 20:33

abney317

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Comments

Derek Wang · Accepted Answer · 2020-09-30 20:33:50Z

2

The difference between a++ and ++a is the value of the expression.

So you can get the result as the question.

answered Sep 30, 2020 at 20:33

Derek Wang

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