index
Returns the index of the current item in the list function, starting from 0.
[1, 2, 3]
.map(
current + index
)/* This is the original list */
[1, 2, 3]
/* 'map' will run operations on each item in that list */
.map(
/* Here the 'current' value (1, 2, etc.) is returned
and added to the 'index' value (0, 1, etc) */
current + index
)