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Cover image for 7 TypeScript Tricks with Enum (and Fruits) ๐Ÿงบ

7 TypeScript Tricks with Enum (and Fruits) ๐Ÿงบ

Arnaud Leymet
Founder, Techpreneur, Solutions Architect
ใƒปUpdated on ใƒป2 min read

Enums are one of the key features of TypeScript.

Relying on basic enums, (numeric and auto-incremented) is standard and the most common use case. Yet Enums can offer much more:


In the rest of this post, let's assume the following code is available:

enum Fruit {
  APPLE = '๐ŸŽ',
  BANANA = '๐ŸŒ',
  CHERRY = '๐Ÿ’',
}
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1. Merge enums

Merging enums is pretty straightforward using the pipe | operator:

enum OtherFruit {
  DATE = 'date',
}

type AnyFruit = Fruit | OtherFruit
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โ–ถ๏ธ Try on TypeScript Playground


2. Enum subsets

Because cherries may not be as tasty as other fruits, let's exclude them:

type YummyFruits = Exclude<Fruit, Fruit.CHERRY>
// => type YummyFruits = Fruit.APPLE | Fruit.BANANA
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โ–ถ๏ธ Try on TypeScript Playground


3. Get the keys of an enum dynamically

This one needs the use of two type operators: keyof and typeof.

type FruitKey = keyof typeof Fruit
// => type FruitKey = "APPLE" | "BANANA" | "CHERRY"

const keys = Object.keys(Fruit) as FruitKey[]
// => ["APPLE", "BANANA", "CHERRY"]
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โ–ถ๏ธ Try on TypeScript Playground


4. Get the values of an enum dynamically

This snippet leverages the Template Literal type operator:

type FruitValue = `${Fruit}`
// => type FruitValue = "๐ŸŽ" | "๐ŸŒ" | "๐Ÿ’"

const values: FruitValue[] = Object.values(Fruit)
// => ["๐ŸŽ", "๐ŸŒ", "๐Ÿ’"]
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โ–ถ๏ธ Try on TypeScript Playground


5. Iterate over an enum keys

Looping through the enum keys is as simple as:

for (let fruit of Object.keys(Fruit)) {
  console.log(fruit)
}
// => APPLE
//    BANANA
//    CHERRY
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โ–ถ๏ธ Try on TypeScript Playground


6. Iterate over an enum values

In the same spirit, looping through the enum values:

for (let fruit of Object.values(Fruit)) {
  console.log(fruit)
}
// => ๐ŸŽ
//    ๐ŸŒ
//    ๐Ÿ’
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โ–ถ๏ธ Try on TypeScript Playground


7. const enum

By default, enums generate a bunch of code when compiled to JavaScript:

var Fruit;
(function (Fruit) {
    Fruit["APPLE"] = "๐ŸŽ";
    Fruit["BANANA"] = "๐ŸŒ";
    Fruit["CHERRY"] = "๐Ÿ’";
})(Fruit || (Fruit = {}));
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There is however a way not to generate this much code: by leveraging const enum.

Adding just a const in front of our Fruit enum makes a big difference:

const enum Fruit {
  APPLE = '๐ŸŽ',
  BANANA = '๐ŸŒ',
  CHERRY = '๐Ÿ’',
}
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...as it compiles to nothing. ๐Ÿ•ณ๏ธ

Just until we use part of its values:

const chosenFruit = Fruit.BANANA
// => compiles to:
// var chosenFruit = "๐ŸŒ";
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โ–ถ๏ธ Try on TypeScript Playground

Discussion (5)

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kgsnaidu profile image
Gowri Sankara Naidu Karri • Edited
type FruitValue = `${Fruit}`
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This is not valid, typescript throwing error here

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prod profile image
Arnaud Leymet Author

I just added TypeScript playground links for each examples.
You'll see that this works just fine :)

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kgsnaidu profile image
Gowri Sankara Naidu Karri

Maybe my local typescript version might not supported. Thanks

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captainyossarian profile image
yossarian

You can also write about const enum

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prod profile image
Arnaud Leymet Author

Indeed; here it is; a brand new part about const enum at the end of the post.