`span()`

Creates an array with the span of numbers going from `first`

and ending at `last`

if possible depending on the specified step value.

{*number*}
**first**

First number to be processed for the returned array.

{*number*}
**last**

Last number to be processed for the returned array.

{*number=*}
**opt_step**
*Optional, Default:*

`1`

Defaults to

`1`

if not given or if `0`

or `NaN`

is specified. The difference between each subsequent number to be processed for the returned array.
{*Function=*}
**opt_mapper**
*Optional*

Function to call for each number in the sequence and whose return value will be used as the value added to the returned array. If specified this function will be called for every number in the span, receiving it as the one and only argument.

{*Array*}

An array containing the sequence of numbers starting at

`first`

and ending at `last`

. If `first`

is less than `last`

and `opt_step`

is less than `0`

or if `last`

is less than `first`

and `opt_step`

is greater than `0`

an empty array will be returned. If `opt_mapper`

is given the array will contain the sequence of mapped.