Function err

Create an instance of Err.

If you need to create an instance with a specific type (as you do whenever you are not constructing immediately for a function return or as an argument to a function), you can use a type parameter:

const notString = err<number, string>('something went wrong');
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Note: passing nothing will produce a Result<T, void>, passing undefined will produce a Result<T, undefined> which is compatible with Result<T, void>.

const normalResult = err<number, string>('oh no');
const explicitUndefined = err<number, undefined>(undefined);
const implicitVoid = err<number, void>();
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In the context of an immediate function return, or an arrow function with a single expression value, you do not have to specify the types, so this can be quite convenient.

const arrowValidate = (data: SomeData): Result<number, string> =>
  isValid(data) ? ok(42) : err('something went wrong');

function fnValidate(data: someData): Result<number, string> {
  return isValid(data) ? ok(42) : err('something went wrong');
}
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Create an instance of Err.

If you need to create an instance with a specific type (as you do whenever you are not constructing immediately for a function return or as an argument to a function), you can use a type parameter:

const notString = err<number, string>('something went wrong');
Copy

Note: passing nothing will produce a Result<T, void>, passing undefined will produce a Result<T, undefined> which is compatible with Result<T, void>.

const normalResult = err<number, string>('oh no');
const explicitUndefined = err<number, undefined>(undefined);
const implicitVoid = err<number, void>();
Copy

In the context of an immediate function return, or an arrow function with a single expression value, you do not have to specify the types, so this can be quite convenient.

const arrowValidate = (data: SomeData): Result<number, string> =>
  isValid(data) ? ok(42) : err('something went wrong');

function fnValidate(data: someData): Result<number, string> {
  return isValid(data) ? ok(42) : err('something went wrong');
}
Copy

Create an instance of Err.

If you need to create an instance with a specific type (as you do whenever you are not constructing immediately for a function return or as an argument to a function), you can use a type parameter:

const notString = err<number, string>('something went wrong');
Copy

Note: passing nothing will produce a Result<T, void>, passing undefined will produce a Result<T, undefined> which is compatible with Result<T, void>.

const normalResult = err<number, string>('oh no');
const explicitUndefined = err<number, undefined>(undefined);
const implicitVoid = err<number, void>();
Copy

In the context of an immediate function return, or an arrow function with a single expression value, you do not have to specify the types, so this can be quite convenient.

const arrowValidate = (data: SomeData): Result<number, string> =>
  isValid(data) ? ok(42) : err('something went wrong');

function fnValidate(data: someData): Result<number, string> {
  return isValid(data) ? ok(42) : err('something went wrong');
}
Copy