Check string value in enum TypeScript

Question

Say there is an

enum ArrowKey{
  Up = "ArrowUp",
  Right = "ArrowRight",
  Down = "ArrowDown",
  Left = "ArrowLeft"
}

Now when receiving a KeyboardEvent with e.key "ArrowUp" how is it easily checked that this string value exists in the enum? And how to pick out the right enum value afterwards?

Because I need the enum value to be passed into a method and this method will have a switch statement for the enum to figure out what to do next. Consider not to downvote when you have such little reputation... — Youp Bernoulli
– Youp Bernoulli, Commented Mar 2, 2018 at 15:50
I don't understand what exactly you're trying to do. You can use e.key directly for your switch because when e.key === 'ArrowUp' then e.key === ArrowKey.Up. You could even consider using a const enum. — Tao
– Tao, Commented Mar 2, 2018 at 16:41
First I would like to check if the string value from e.key which is "ArrowUp" exists as an enum value in the ArrowKey enum. If so, I would like to get the corresponding enum value -> ArrowKey.up — Youp Bernoulli
– Youp Bernoulli, Commented Mar 2, 2018 at 16:43

Wilhelm Olejnik · Accepted Answer · 2018-03-15 17:59:20Z

7

The following function will return enum value corresponding to pressed arrow key or null if this key is not defined inside that enum.

getEnumValue(event): ArrowKey | null {
  const pressedKey = event.key;
  const keyEnum = Object.keys(ArrowKey).find(key => ArrowKey[key] === pressedKey);
  return ArrowKey[keyEnum] || null;
}

demo: https://stackblitz.com/edit/angular-dmqwyf?embed=1&file=app/app.component.html

EDIT: one-line equivalent (ES 2017)

getEnumValue(event): ArrowKey | null {
  return Object.values(ArrowKey).includes(event.key) ? event.key : null;
}

edited Mar 15, 2018 at 17:59

answered Mar 2, 2018 at 17:06

Wilhelm Olejnik

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2 Comments

jlogan Over a year ago

You might need to typecast for that second suggestion given that event.key is going to return a string not an ArrowKey

Benny Halperin Over a year ago

@jlogan you are right. Should be:

getEnumValue(event): ArrowKey | null {   return Object.values(ArrowKey).includes(event.key as ArrowKey) ? event.key : null; }

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