JS while loop array[i++]. How does it work?

Question

I'm wondering how it works. I guess that "right[r++]" increments "r" in while loop. Or it shows which element of "right" we push to "result"?

function merge(left, right){
  var result = [],
      lLen = left.length,
      rLen = right.length,
      l = 0,
      r = 0;
  while(l < lLen && r < rLen){
     if(left[l] < right[r]){
       result.push(left[l++]);
     }
     else{
       result.push(right[r++]);
    }
  }  
  return result.concat(left.slice(l)).concat(right.slice(r));
}

Thank you.

Answer 1

result.push(right[r++]);

is essentially shorthand for

result.push(right[r]);
r = r + 1;

The ++ operator after the variable returns the variable's value before it gets incremented.

For comparison, using it before the variable

result.push(right[++r]);

would achieve the same result as

r = r + 1;
result.push(right[r]);