Optionalvalue: string | number | boolean | nullThe value to start at. The argument type depends on which
orderBy*() function was used in this query. Specify a value that matches
the orderBy*() type. When used in combination with orderByKey(), the
value must be a string.
Optionalkey: stringThe child key to start at. This argument is only allowed if ordering by child, value, or priority.
Creates a QueryConstraint with the specified starting point.
Using
startAt(),startAfter(),endBefore(),endAt()andequalTo()allows you to choose arbitrary starting and ending points for your queries.The starting point is inclusive, so children with exactly the specified value will be included in the query. The optional key argument can be used to further limit the range of the query. If it is specified, then children that have exactly the specified value must also have a key name greater than or equal to the specified key.