In Typescript, how can we reverse the order of an enum

Question

In Typescript, how can we reverse the order of an enum

I am encountering a particular challenge with the following code snippet:

enum MyEnum {
  Colors = 'AreColors',
  Cars = 'AreCars',
}

const menuTitle = ((obj: MyEnum) => {
  const newObj = {};
  Object.keys(obj).forEach((x) => {
    newObj[obj[x]] = x;
  });
  return newObj;
});

My objective is to switch the enum keys with their corresponding values within the code.
However, this leads to an issue stating

Element implicitly has an 'any' type because expression of type 'string' can't be used to index type '{}'

at this line newObj[obj[x]] = x;.
Could you please explain why this problem occurs and suggest potential solutions?

javascript typescript

Answer 1

Answer №1

There seem to be a few issues with the code you provided:

If you intend to reverse the key-value pairs of the enum by passing in MyEnum as the object, then you should use obj: typeof MyEnum. This assumes that you want to utilize menuTitle(MyEnum) for this purpose.
Object.keys(obj) will return an array of strings, which can cause problems when indexing your enum. To resolve this, cast it to an array of keyof typeof MyEnum.

Here is an improved version of the code:

enum MyEnum {
  Colors = 'AreColors',
  Cars = 'AreCars',
}

const menuTitle = ((obj: typeof MyEnum) => {
  const newObj: { [key in MyEnum]?: keyof typeof MyEnum } = {};
  (Object.keys(obj) as Array<keyof typeof MyEnum>).forEach((x) => {
    newObj[obj[x]] = x;
  });
  return newObj;
});

console.log(menuTitle(MyEnum));

You can view a proof-of-concept example on the TypeScript Playground.

Answer 2

There seem to be a few issues with the code you provided:

If you intend to reverse the key-value pairs of the enum by passing in MyEnum as the object, then you should use obj: typeof MyEnum. This assumes that you want to utilize menuTitle(MyEnum) for this purpose.
Object.keys(obj) will return an array of strings, which can cause problems when indexing your enum. To resolve this, cast it to an array of keyof typeof MyEnum.

Here is an improved version of the code:

enum MyEnum {
  Colors = 'AreColors',
  Cars = 'AreCars',
}

const menuTitle = ((obj: typeof MyEnum) => {
  const newObj: { [key in MyEnum]?: keyof typeof MyEnum } = {};
  (Object.keys(obj) as Array<keyof typeof MyEnum>).forEach((x) => {
    newObj[obj[x]] = x;
  });
  return newObj;
});

console.log(menuTitle(MyEnum));

You can view a proof-of-concept example on the TypeScript Playground.

In Typescript, how can we reverse the order of an enum

Answer №1

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