io-ts-reporters

Currently this package only includes one reporter. The output is an array of strings in the format of:

Expecting ${expectedType} at ${path} but instead got: ${expectedType}

And for union types:

Expecting one of:
    ${unionType1}
    ${unionType2}
    ${...}
    ${unionTypeN}
at ${path} but instead got: ${actualValue}

Example

import * as t from 'io-ts'
import reporter from 'io-ts-reporters'

const User = t.interface({name: t.string})

// When decoding fails, the errors are reported
reporter.report(User.decode({nam: 'Jane'}))
//=> ['Expecting string at name but instead got: undefined']

// Nothing gets reported on success
reporter.report(User.decode({name: 'Jane'}))
//=> []

To only format the validation errors in case the validation failed (ie. mapLeft) use formatValidationErrors instead.

import * as t from 'io-ts'
import {formatValidationErrors} from 'io-ts-reporters'
import * as E from 'fp-ts/Either'
import {pipe} from 'fp-ts/pipeable'

const User = t.interface({name: t.string})

const result = User.decode({nam: 'Jane'}) // Either<t.Errors, User>

E.mapLeft(formatValidationErrors)(result) // Either<string[], User>

For more examples see the tests.

Credits

This library was created by OliverJAsh.