CODE EXAMPLE FOR JAVASCRIPT

use index of an array within a for loop

const logArrayElements = (element, index, array) => {
  console.log('a[' + index + '] = ' + element);
};

// Notice that index 2 is skipped, since there is no item at
// that position in the array...
[2, 5,, 9].forEach(logArrayElements);
// logs:
// a[0] = 2
// a[1] = 5
// a[3] = 9