enum_typescript.ts

enum_typescript.ts

/* 
In this article, we reviewed a few ways to iterate over the keys and values of enum types 
in TypeScript. First, we used the inbuilt methods of any TypeScript object, noting that
they are fairly “low-level”.

Second, we moved to a higher-level approach, with for loops. We verified that we can teach
TypeScript to preserve the typing given by enums, without relying on the string or numeric
representation.
*/
enum TrafficLight {
  Green,
  Yellow,
  Red
}

Object.keys(TrafficLight).forEach((key, index) => {
  console.log(`[TrafficLight:Object.keys] ${key} has index ${index}`)
})

Object.values(TrafficLight).forEach((value, index) => {
  console.log(`[TrafficLight:Object.values] ${Object.keys(TrafficLight)[index]} - ${value} has index ${index}`)
})

for (const tl in TrafficLight) {
  const value = TrafficLight[tl]
  if (typeof value === "string") {
    console.log(`[TrafficLight:for] Value: ${TrafficLight[tl]}`)
  }
}

/* -------------------------------------- */

enum StarRating {
  TooBad,
  Bad,
  Neutral,
  Good,
  VeryGood
}

function enumKeys<O extends object, K extends keyof O = keyof O> (obj: O): K[] {
  return Object.keys(obj).filter(k => !Number.isNaN(k)) as K[]
}

for (const tl of enumKeys(StarRating)) {
  const value = StarRating[tl]
  if (typeof value === "string") {
    console.log(`[StarRating:enumKeys] Value: ${StarRating[tl]}`)
  }
}