With Typescript, is it possible to define a type of a float (number) that's between 0 and 1 inclusively?
If this isn't possible at all, a way to define the type of an integer between 0 and 100 inclusively.
1 Answers
Defining the type of an integer between 0 and 100 is trivial, albeit tedious
type IntBetween0And100 = 0 | 1 | 2 | 3 | 4 | 5 | ...
The same thing for floats, not so easy.
I would approach the problem by making use of smart constructors. The idea is quite simple, you shift the responsibility of ensuring that a value is of the correct type from the type system (which is unable to do it) to the runtime.
A simplified example might look like this.
type Option<T> = null | T // a simplified Option monad
type FloatBetween0And100 = number
const isFloatBetween0And100 = (n: unknown): n is FloatBetween0And100 => typeof n === 'number' && n <= 100 && n >= 0
const makeFloatBetween0And100 = (n: number): Option<FloatBetween0And100> => isFloatBetween0And100(n) ? n : null
The article I linked above goes a lot more in detail about this approach, check it out.
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