TakeWhile

TakeWhile[list, crit] gives elements ei from the beginning of list, continuing so long as crit[ei] is True.

Examples

Take while positive:

TakeWhile[{1, 2, 3, -1, 4, 5}, Positive]
(* {1, 2, 3} *)

Take while less than 5:

TakeWhile[{1, 3, 5, 7, 9}, # < 5 &]
(* {1, 3} *)

Please visit the official Wolfram Language Reference for more details.