Why is it bad pratice calling an array index with a variable?

Question

I\'m currently developing a little game in Javascript and I\'m using Codacy to review my code and help me cleaning it.

One of the most seen error is Generic O

Answer 1

What is bad in accessing by index: there might be no element at that index.

Regarding your code, I would make a preset map:

const preset = {
  0: 0.5,
  1: 1.5,
  2: 2,
  3: 3
};

And then use it in function:

function sellPotato(x, player) {
  // This additional check gives you more confidence in accessing element of and array by index
  if (player.inventory.length < x) return;

  if (preset[player.inventory[x].value]) {
    player.money += player.inventory[x].price * preset[player.inventory[x].value];
  }
  player.inventory.splice(x, 1);
  display(player);
}