Question

I’ve a simple FOR statement like this:

var num = 10,
    reverse = false;

for(i=0;i<num;i++){
    console.log(i);
}

when reverse is false I want it to return something like [0,1,2,3,4,5,6,7,8,9]

but, when reverse is true, it should return [9,8,7,6,5,4,3,2,1,0]

Which is the most efficient way to get this result, without checking every time if reverse is true or false inside the loop?

I don’t want to do this:

var num = 10,
    reverse = false;

for(i=0;i<num;i++){
    if(reverse) console.log(num-i)
    else console.log(i)
}

I would like to check reverse only one time outside the loop.

Answer 1

var num = 10,
reverse = false;

if(!reverse) for( var i=0;i<num;i++) log(i);
else         while(num-- )      log(num);

   // to avoid duplication if the code gets long
function log( num ) { console.log( num ); }

---

EDIT:

As noted in the comments below, if i is not declared elsewhere and you do not intend for it to be global, then declare it with the other variables you declared.

And if you don’t want to modify the value of num, then assign it to i first.

var num = 10,
reverse = false,
i;

if(!reverse) for(var i=0;i<num;i++) log(i);   // Count up
else         {var i=num; while(i--) log(i);}  // Count down

function log( num ) { console.log( num ); }