A new .pipe() method on Decoder allows you to pass the output of one decoder into another:
```
string
  .transform((s) => s.split(',')) // transform first...
  .pipe(array(nonEmptyString)); //   ...then validate that result
```
This was previously possible already with .then, but it wasn't as elegant to express.

The new .pipe() can also dynamically select another decoder, based on the input:

string
  .transform((s) => s.split(',').map(Number)) // transform first...
  .pipe((tup) =>
    tup.length === 2
      ? point2d
      : tup.length === 3
        ? point3d
        : never('Invalid coordinate'),
  );

Decoder error messages will now quote identifiers using single quotes, which makes them more human-readable in JSON responses. Compare:
```
"Value at key \"foo\": Must be \"bar\", \"qux\""  // ❌ Previously
"Value at key 'foo': Must be 'bar', 'qux'"        // ✅ Now
```
Some runtime perf optimizations

New decoders:

identifier (docs)
nanoid() (docs)

Removed decoders:

Remove numericBoolean decoder, which was deprecated since 2.3.0.

Readme

Source

Elegant and battle-tested validation library for type-safe input data for TypeScript.

Introduction

Data entering your application from the outside world should not be trusted without validation and often is of the any type, effectively disabling your type checker around input values. It's an industry good practice to validate your expectations right at your program's boundaries. This has two benefits: (1) your inputs are getting validated, and (2) you can now statically know for sure the shape of the incoming data. Decoders help solve both of these problems at once.

Basic example

import { array, iso8601, number, object, optional, string } from 'decoders';

// Incoming data at runtime
const externalData = {
  id: 123,
  name: 'Alison Roberts',
  createdAt: '1994-01-11T12:26:37.024Z',
  tags: ['foo', 'bar'],
};

// Write the decoder (= what you expect the data to look like)
const userDecoder = object({
  id: number,
  name: string,
  createdAt: optional(iso8601),
  tags: array(string),
});

// Call .verify() on the incoming data
const user = userDecoder.verify(externalData);
//    ^^^^
//    TypeScript automatically infers this type as:
//    {
//      id: number;
//      name: string;
//      createdAt?: Date;
//      tags: string[];
//    }

Installation

npm install decoders

Requirements

You must set strict: true in your tsconfig.json in order for type inference to work correctly!

// tsconfig.json
{
  "compilerOptions": {
    "strict": true
  }
}

Documentation

Documentation can be found on https://decoders.cc.

Building your own decoders

There is a dedicated page in the docs that explains how to build your own decoders — it’s fun!

Keywords

FAQs

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Last updated on 21 Jan 2024

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