CodeSOD: Literal Type Checking

Validating your inputs is important, even when the sender is an API- in the land of JSON-based data exchange, we can't guarantee which keys exist without checking.

Philipp's team uses the "Runtypes" library to solve this problem. It lets them write code like this:

r.Array(r.Record({ id: r.Number, name: r.String })).check(inputData)

This verifies that inputData is an array of objects with id fields (containing numbers), and a name field (containing strings).

For more complex validation, Runtypes lets you use add constraint functions to your types. So, for example, if you wanted to ensure a number is in the range of 0-52, you could do:

const YearIndexes = r.Number.withConstraint((n) => n >= 0 && n <= 52);

You could do that. But Phillip's co-worker wanted to find a more declarative approach that doesn't have any of those pesky function calls in it.

const YearIndexes = Union( Literal('0'), Literal('1'), Literal('2'), Literal('3'), Literal('4'), Literal('5'), Literal('6'), Literal('7'), Literal('8'), Literal('9'), Literal('10'), Literal('11'), Literal('12'), Literal('13'), Literal('14'), Literal('15'), Literal('16'), Literal('17'), Literal('18'), Literal('19'), Literal('20'), Literal('21'), Literal('22'), Literal('23'), Literal('24'), Literal('25'), Literal('26'), Literal('27'), Literal('28'), Literal('29'), Literal('30'), Literal('31'), Literal('32'), Literal('33'), Literal('34'), Literal('35'), Literal('36'), Literal('37'), Literal('38'), Literal('39'), Literal('40'), Literal('41'), Literal('42'), Literal('43'), Literal('44'), Literal('45'), Literal('46'), Literal('47'), Literal('48'), Literal('49'), Literal('50'), Literal('51'), Literal('52'), // this is the maximal amount of years prospect can be insured for in the range 18-70 years.);

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