Error Formatting

Built-in formatters to create human-readable error messages from decoder rejections

Decoders provides built-in formatters to create human-readable error messages.

formatInline (default)

The default formatter used by .verify(). Echoes back the full input with errors annotated inline:

import { object, string, number, formatInline } from 'decoders';

const userDecoder = object({
  id: number,
  name: string,
  email: string,
});

const result = userDecoder.decode({
  id: '123',
  name: 'Alice',
  email: 42,
});

if (!result.ok) {
  console.log(formatInline(result.error));
  // {
  //   id: "123",
  //       ^^^^^ Must be number
  //   name: "Alice",
  //   email: 42,
  //          ^^ Must be string
  // }
}

formatShort

Provides concise, line-by-line error summaries. Useful when you want compact messages, or when security is a concern and you want to avoid echoing back sensitive input data.

import { object, string, formatShort } from 'decoders';

const credentials = object({
  user: string,
  password: string,
});

const result = credentials.decode({
  user: 123,
  password: 'p@ssw0rd',
});

if (!result.ok) {
  console.log(formatShort(result.error));
  // Value at key "user": Must be string
}

Avoid using formatInline when decoding sensitive inputs, as it echoes back the full input:

{
  user: 123,
        ^^^ Must be string
  password: "p@ssw0rd"
}

When using Standard Schema

When using decoders via Standard Schema, errors are returned as an issue list:

import { object, string, number } from 'decoders';

const userDecoder = object({
  name: string,
  age: number,
});

const result = userDecoder['~standard'].validate({ name: 'Alison', age: '33' });
// {
//   issues: [
//     { message: 'Must be number', path: ['age'] },
//   ]
// }

formatInline (default)

formatShort

When using Standard Schema

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