span()Creates an array with the span of numbers going from first and ending at last if possible depending on the specified step value.
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1 if not given or if 0 or NaN is specified. The difference between each subsequent number to be processed for the returned array.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.