_.indexOf

indexOf_.indexOf(array, value, [isSorted])
Returns the index at which value can be found in the array, or -1 if value is not present in the array. If you're working with a large array, and you know that the array is already sorted, pass true for isSorted to use a faster binary search ... or, pass a number as the third argument in order to look for the first matching value in the array after the given index.

_.indexOf([1, 2, 3], 2);
=> 1