Preheat oven to 350°. Place cranberries, dates, and water in a saucepan; bring to a boil over medium heat. Reduce heat; simmer, covered, until berries pop, about 15 minutes, stirring occasionally. Remove from heat; stir in vanilla.
Mix flour, oats, brown sugar, baking soda, and salt; stir in melted butter. Press half of the mixture into an ungreased 13x9-in. pan. Bake 8 minutes.
Spoon cranberry mixture over crust. Sprinkle with remaining oat mixture; pat down gently. Bake until golden brown, 25-30 minutes. Cool completely on a wire rack.