Javascript: Generic get next item in array

I think that an object could be probably a better data structure for this kind of task

items = {
  ball : "1f7g",
  spoon: "2c8d", 
  pen  : "9c3c"
}


console.log(items['ball']); // 1f7g

Cycled items from array this might be useful

const currentIndex = items.indexOf(currentItem);
const nextIndex = (currentIndex + 1) % items.length;
items[nextIndex];

The first item will be taken from the beginning of the array after the last item

Try this String.prototype function:

String.prototype.cycle = function(arr) {
  const i = arr.indexOf(this.toString())
  if (i === -1) return undefined
  return arr[(i + 1) % arr.length];
};

Here is how you use it:

"a".cycle(["a", "b", "c"]); // "b"
"b".cycle(["a", "b", "c"]); // "c"
"c".cycle(["a", "b", "c"]); // "a"
"item1".cycle(["item1", "item2", "item3"]) // "item2"

If you want to do it the other way round, you can use this Array.prototype function:

Array.prototype.cycle = function(str) {
  const i = this.indexOf(str);
  if (i === -1) return undefined;
  return this[(i + 1) % this.length];
};

Here is how you use it:

["a", "b", "c"].cycle("a"); // "b"
["a", "b", "c"].cycle("b"); // "c"
["a", "b", "c"].cycle("c"); // "a"
["item1", "item2", "item3"].cycle("item1") // "item2"

You've almost got it right, but the syntax is arr[x], not arr(x):

index = array.indexOf(value);
if(index >= 0 && index < array.length - 1)
   nextItem = array[index + 1]

BTW, using an object instead of an array might be a better option:

data = {"ball":"1f7g", "spoon":"2c8d", "pen":"9c3c"}

and then simply

code = data[name]