How to retrieve enums in TypeScript without including them

Question

How to retrieve enums in TypeScript without including them

In TypeScript, to work with a subset of items in an enum, we typically do the following:

enum Operator {
  EQUAL = 'EQUAL',
  NOT_EQUAL = 'NOT_EQUAL',
  LESS = 'LESS',
  GREATER = 'GREATER',
}

type EqualOperators = Exclude<Operator, Operator.LESS | Operator.GREATER>

I'm wondering if there's a way to convert EqualOperators from a type to an enum, so that I can use it directly in a script?

By "use it in a script," I mean being able to access the enum values within a JavaScript function. This is not possible with types. For example:

enum Operator {
  EQUAL = 'EQUAL',
  NOT_EQUAL = 'NOT_EQUAL',
  LESS = 'LESS',
  GREATER = 'GREATER',
}

function getOperator() {
  if (Operator.EQUAL) {
    return "=";
  }
  if (Operator.NOT_EQUAL) {
    return "!=";
  }

  throw new Error('Invalid operator');
}

Any suggestions or solutions would be greatly appreciated. Thank you!

typescript

Answer 1

Answer №1

Typescript enums serve as both types and objects. While types and interfaces disappear at runtime, objects remain. This means that in order to use a condition like if (op === Operator.EQUAL), the Operator must exist at runtime because we are utilizing the object aspect of the enum.

In your scenario, the Operators "object" functions similarly to this:

{
  EQUAL: 'EQUAL',         
  NOT_EQUAL: 'NOT_EQUAL', 
  LESS: 'LESS',           
  GREATER: 'GREATER',     
}

If you want to create an object using TypeScript's type system based on the enum, you need to instantiate an object alongside it. One approach is to define a new type called EqualOperators which ensures that each key is assigned the correct value from the original enum.

type EqualOperators = Omit<typeof Operator, 'LESS' | 'GREATER'>;

const EqualOperators: EqualOperators = {
  EQUAL: Operator.EQUAL,
  NOT_EQUAL: Operator.NOT_EQUAL,
}

An alternative method could be to use the Pick utility type instead for defining EqualOperators:

type EqualOperators = Pick<typeof Operator, 'EQUAL' | 'NOT_EQUAL'>;

This approach clearly specifies the "equality" operators, making it easier to maintain when adding new elements. Ultimately, choosing a method depends on how often the original enum changes and what elements are likely to be added in the future.

Answer 2

Typescript enums serve as both types and objects. While types and interfaces disappear at runtime, objects remain. This means that in order to use a condition like if (op === Operator.EQUAL), the Operator must exist at runtime because we are utilizing the object aspect of the enum.

In your scenario, the Operators "object" functions similarly to this:

{
  EQUAL: 'EQUAL',         
  NOT_EQUAL: 'NOT_EQUAL', 
  LESS: 'LESS',           
  GREATER: 'GREATER',     
}

If you want to create an object using TypeScript's type system based on the enum, you need to instantiate an object alongside it. One approach is to define a new type called EqualOperators which ensures that each key is assigned the correct value from the original enum.

type EqualOperators = Omit<typeof Operator, 'LESS' | 'GREATER'>;

const EqualOperators: EqualOperators = {
  EQUAL: Operator.EQUAL,
  NOT_EQUAL: Operator.NOT_EQUAL,
}

An alternative method could be to use the Pick utility type instead for defining EqualOperators:

type EqualOperators = Pick<typeof Operator, 'EQUAL' | 'NOT_EQUAL'>;

This approach clearly specifies the "equality" operators, making it easier to maintain when adding new elements. Ultimately, choosing a method depends on how often the original enum changes and what elements are likely to be added in the future.

Answer 3

Answer №2

To achieve this, follow the steps outlined below:

enum Operation {
  ADD = 'ADD',
  SUBTRACT = 'SUBTRACT',
  MULTIPLY = 'MULTIPLY',
  DIVIDE = 'DIVIDE',
}

const BasicOperations = Operation as Omit<typeof Operation, "MULTIPLY" | "DIVIDE">;
type BasicOperations = typeof BasicOperations[keyof typeof BasicOperations];

Answer 4

To achieve this, follow the steps outlined below:

enum Operation {
  ADD = 'ADD',
  SUBTRACT = 'SUBTRACT',
  MULTIPLY = 'MULTIPLY',
  DIVIDE = 'DIVIDE',
}

const BasicOperations = Operation as Omit<typeof Operation, "MULTIPLY" | "DIVIDE">;
type BasicOperations = typeof BasicOperations[keyof typeof BasicOperations];

Answer 5

Answer №3

An enumeration serves as both a data type and a set of fixed values, demonstrated in the code snippet below:

enum Operation {
  ADD = 'ADD',
  SUBTRACT = 'SUBTRACT',
  MULTIPLY = 'MULTIPLY',
  DIVIDE = 'DIVIDE',
}

function getOperation(op: Operation) {
  if (op == Operation.ADD) {
    return "+";
  }
  if (op == Operation.SUBTRACT) {
    return "-";
  }
  if (op == Operation.MULTIPLY) {
    return "*";
  }
  if (op == Operation.DIVIDE){
    return "/";
  }

  throw new Error('invalid operation');
}

console.log(getOperation(Operation.ADD));
console.log(getOperation(Operation.SUBTRACT));
console.log(getOperation(Operation.MULTIPLY));
console.log(getOperation(Operation.DIVIDE));
console.log(getOperation('wrong')); // error
console.log(getOperation('wrong' as any)); // works but will throw an error when running

Playground link

Answer 6

An enumeration serves as both a data type and a set of fixed values, demonstrated in the code snippet below:

enum Operation {
  ADD = 'ADD',
  SUBTRACT = 'SUBTRACT',
  MULTIPLY = 'MULTIPLY',
  DIVIDE = 'DIVIDE',
}

function getOperation(op: Operation) {
  if (op == Operation.ADD) {
    return "+";
  }
  if (op == Operation.SUBTRACT) {
    return "-";
  }
  if (op == Operation.MULTIPLY) {
    return "*";
  }
  if (op == Operation.DIVIDE){
    return "/";
  }

  throw new Error('invalid operation');
}

console.log(getOperation(Operation.ADD));
console.log(getOperation(Operation.SUBTRACT));
console.log(getOperation(Operation.MULTIPLY));
console.log(getOperation(Operation.DIVIDE));
console.log(getOperation('wrong')); // error
console.log(getOperation('wrong' as any)); // works but will throw an error when running

Playground link

How to retrieve enums in TypeScript without including them

Answer №1

Answer №2

Answer №3

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