How to define a regex-matched string type in Typescript?

Question

Is it possible to define an interface which has some information on the format of a string? Take the following example:

interface timeMarkers{     markerTime: string[]         }; 

an example would be:

{    markerTime: ["0:00","1:30", "1:48"]                    } 

My question: Is there a way to define the type for markerTime such that that the string value must always match this regex, instead of declaring it as simply string[] and going from there?

var reg = /[0-9]?[0-9]:[0-9][0-9]/;

Answer 1

There is no way to define such a type. There is a proposal on GitHub to support this, but it currently does not appear to be a priority. Vote on it and maybe the team might include it in a future release.

Edit

Starting in 4.1 you can define a type that would validate the string without actually defining all the options:

type MarkerTime =`${number| ''}${number}:${number}${number}`  let a: MarkerTime = "0-00" // error let b: MarkerTime = "0:00" // ok let c: MarkerTime = "09:00" // ok  

Playground Link

Answer 2

Until regex types become available to the language, you can now use template literal types in TS 4.1.

Let me refer to the question example and illustrate, how to model a time restricted string type called Time. Time expects strings in the format hh:mm (e.g. "23:59") here for simplification.

Step 1: define HH and MM types

Paste following code into your browser web console:

Array.from({length:24},(v,i)=> i).reduce((acc,cur)=> `${acc}${cur === 0 ? "" : "|"}'${String(cur).padStart(2, 0)}'`, "type HH = ") Array.from({length:60},(v,i)=> i).reduce((acc,cur)=> `${acc}${cur === 0 ? "" : "|"}'${String(cur).padStart(2, 0)}'`, "type MM = ") 

Generated result, which we can use as types in TS:

type HH = '00'|'01'|'02'|'03'|'04'|'05'|'06'|'07'|...|'22'|'23' type MM = '00'|'01'|'02'|'03'|'04'|'05'|'06'|'07'|...|'58'|'59' 

Step 2: Declare Time

type Time = `${HH}:${MM}` 

Simple as that.

Step 3: Some testing

const validTimes: Time[] = ["00:00","01:30", "23:59", "16:30"] const invalidTimes: Time[] = ["30:00", "23:60", "0:61"] // all emit error 

Here is a live code example to get play around with Time.