io-ts-human-reporter

Customizable and _smart_ io-ts error reporting.

Have you ever got yourself into position that you wanted to present io-ts validation
errors to actual end users?\
Or perhaps, your types are quite complex and error messages are not really helpful even during development?\
Or maybe you are just looking for a customizable way to display missing or invalid fields on API request payloads?

If the answer for any of the above questions is yes - I think I got you covered.

goal

Provide human-friendly error messages based on io-ts validation. So human friendly,
that you could even show them to anyone having basic idea about json.

usage/examples

``bash
npm i io-ts-human-reporter


fp-ts and io-ts are package peerDependencies

so make sure you have these also installed

`

`ts
import * as t from 'io-ts';
import { report, reportOne } from 'io-ts-humman-reporter';

const codec = t.type({
root: t.type({
a: t.number,
b: t.string,
c: t.union([
t.type({ c1: t.string, c2: t.string }),
t.type({ d1: t.string, d2: t.string }),
]),
}),
});

const validation = codec.decode({ root: { a: 1, b: '', c: { d1: 1 } } });

report(validation);
// [
// "got '1' expected 'string' at 'root.c.d1'",
// "missing property 'd2' at 'root.c'",
// ]

reportOne(validation);
// "got '1' expected 'string' at 'root.c.d1'"
`

features

- ### _smart_ handling of unions

errors will be reported only from the variant which has the most in common with the given input

`ts
const codec = t.union([t.type({ a: t.number, b: t.null }), t.type({ c: t.string, d: t.number })]);

const data = { c: null };

report(codec.decode(data));
// [
// "got null expected 'string' at 'c'",
// "missing property 'd' at ''",
// ]
`

- ### message customization

e.g. for translations

`ts
const codec = t.type({ a: t.number, b: t.null });
const data = { a: '11' };

report(codec.decode(data), {
messages: {
missing: (keys, path) =>
YOINKS! You forgot to add "${keys.join(',')}" at "${path.join('/')}".,
},
});
// [
// "got 11 expected 'number' at 'a'",
// 'YOINKS! You forgot to add "b" at "."'
// ]
`

- ### short-circuiting report of the first error

for greater efficiency on huge objects

`ts
const codec = t.type({ a: t.number, b: t.null });

reportOne(codec.decode({ a: '11' }));
// "got 11 expected 'number' at 'a'"
reportOne(codec.decode({ a: 11, b: null }));
// null
`

- ### respecting custom codec names

`ts
const codec = t.type({ a: t.number, b: t.null }, 'FooBar');
const data = null;

report(codec.decode(data));
// [
// "got null expected 'FooBar' at ''"
// ]
``