Difference between pre-increment and post-increment in a loop?

Question

Is there a difference in ++i and i++ in a for loop? Is it simply a syntax thing?

Answer 1

Yes, there is a difference between ++i and i++ in a for loop, though in unusual use cases; when a loop variable with increment/decrement operator is used in the for block or within the loop test expression, or with one of the loop variables. No it is not simply a syntax thing.

As i in a code means evaluate the expression i and the operator does not mean an evaluation but just an operation;

• ++i means increment value of i by 1 and later evaluate i,
• i++ means evaluate i and later increment value of i by 1.

So, what are obtained from each two expressions differ because what is evaluated differs in each. All same for --i and i--

For example;

let i = 0

i++ // evaluates to value of i, means evaluates to 0, later increments i by 1, i is now 1
0
i
1
++i // increments i by 1, i is now 2, later evaluates to value of i, means evaluates to 2
2
i
2

In unusual use cases, however next example sounds useful or not does not matter, it shows a difference

for(i=0, j=i; i<10; j=++i){
    console.log(j, i)
}

for(i=0, j=i; i<10; j=i++){
    console.log(j, i)
}