Lets say, in a for loop, i am accessing 2 indexes of an array say x and x+1, and comparing those two things to find out how often the numbers of the array increase or decrease.

Is it more/less/equally efficient to have a variable outside of the loop that i reassign each loop, or simply just access it by index inside the loop?

Such as

  let count = 0;

  
  let previousNum = data[0];

  for (let i = 1; i < data.length; i++) {
    const currentNum = data[i];


    if (currentNum > previousNum) {
      count++;
    }

    previousNum = currentNum;
  }

versus

  let count = 0;

  for (let i = 1; i < d.length; i++) {
    const firstNum = data[i - 1];
    const secondNum = data[i];

    if (secondNum > firstNum) {
      count++;
    }
  }

Like on a fundamental level, when it is accessing these indexes, is it iterating through the array to reach the value for these indexes or is it accessing them directly? By accessing only one index inside the loop vs 2 am i increasing the efficiency of the code or is it no difference?