# assert-options

> Generic options parameter handling.

Latest version **0.8.3** (published 2025-03-21) · MIT license · 0 weekly downloads

## Install

```sh
npm install assert-options
pnpm add assert-options
yarn add assert-options
bun add assert-options
```

## Health

**Score 35/100 (D)** — status: maintenance-mode.

Positive: has types; no vulnerabilities; high quality score.

Warnings: low downloads; no esm support; pre 1.0.

Negative: stale; low maintenance score.

## Facts

| | |
|---|---|
| Version | 0.8.3 |
| Published | 2025-03-21 |
| First published | 2019-02-26 |
| Weekly downloads | 0 |
| License | MIT |
| TypeScript types | bundled |
| Module format | CommonJS |
| Node | >=14.0.0 |
| Dependencies | 0 |
| Unpacked size | 11.1 KB |
| Known vulnerabilities | 0 |
| Install scripts | no |
| GitHub stars | 4 |
| Author | Vitaly Tomilov |
| Maintainers | vitaly.tomilov |
| Keywords | assert, options |

## Links

- npm: https://www.npmjs.com/package/assert-options
- Repository: https://github.com/vitaly-t/assert-options
- Issues: https://github.com/vitaly-t/assert-options/issues
- npm.io page: https://npm.io/package/assert-options

## Recent versions

- 0.8.3 (latest) — 2025-03-21
- 0.0.1 (beta) — 2019-02-26
- 0.8.2 — 2024-10-11
- 0.8.1 — 2023-03-18
- 0.8.0 — 2022-11-17
- 0.7.0 — 2020-12-20
- 0.6.2 — 2020-05-02
- 0.6.1 — 2020-02-02
- 0.6.0 — 2019-08-27
- 0.5.0 — 2019-08-26
- 0.4.0 — 2019-07-26
- 0.3.0 — 2019-07-25
- 0.2.0 — 2019-07-25
- 0.1.3 — 2019-03-02
- 0.1.2 — 2019-02-28
- … 9 more at https://npm.io/package/assert-options/versions

## README

assert-options
--------------

[![Build Status](https://github.com/vitaly-t/assert-options/actions/workflows/ci.yml/badge.svg)](https://github.com/vitaly-t/assert-options/actions/workflows/ci.yml)
[![Node Version](https://img.shields.io/badge/nodejs-18%20--%2022-green.svg?logo=node.js&style=flat)](https://nodejs.org)

Smart `options`-object handling, with one line of code:

* throw detailed error on invalid options
* set default values for missing options  

Strongly-typed, built with TypeScript 5.x `strict` mode, for JavaScript clients.

## Rationale

* Passing in invalid or misspelled option names is one of the most common errors in JavaScript.
* Assigning defaults is the most common operation for methods that take options.  

This module automates proper options handling - parsing + setting defaults in one line.

Although this library is implemented in TypeScript, its objective is mainly to help JavaScript clients,
because TypeScript itself can handle invalid options and defaults natively. 

## Installation

```
$ npm i assert-options
```

## Usage

```js
const { assertOptions } = require('assert-options');

function functionWithOptions(options) {
    options = assertOptions(options, {first: 123, second: null});
    
    // options is a safe object here, with all missing defaults set.
}
```

When default values are not needed, you can just use an array of strings:

```js
function functionWithOptions(options) {
    options = assertOptions(options, ['first', 'second']);
    
    // the result is exactly the same as using the following:
    // options = assertOptions(options, {first: undefined, second: undefined});
    
    // options is a safe object here, without defaults.
}
```

You can override how errors are thrown, by creating the `assert` function yourself,
and specifying a custom handler:

```js
const {createAssert} = require('assert-options');

// must implement IOptionsErrorHandler protocol
class MyErrorHanler {
    handle(err, ctx) {
        // throw different errors, based on "err"
        // for reference, see DefaultErrorHandler implementation 
    }
}

const assert = createAssert(new MyErrorHanler());
```

## API

### `assertOptions(options, defaults)` 

* When `options` is `null`/`undefined`, new `{}` is returned, applying `defaults` as specified.

* When `options` contains an unknown property, [Error] `Option "name" is not recognized.` is thrown.

* When a property in `options` is missing or `undefined`, its value is set from the `defaults`,
provided it is available and its value is not `undefined`.

* When `options` is not `null`/`undefined`, it must be of type `object`, or else [TypeError] is thrown:
`Invalid "options" parameter: value`.
  
* Parameter `defaults` is required, as a non-`null` object or an array of strings, or else [TypeError]
is thrown: `Invalid "defaults" parameter: value`.

### `createAssert(handler)`

Creates a new assert function, using a custom error handler that implements `IOptionsErrorHandler` protocol.

For example, the default `assertOptions` is created internally like this:

```js
const {createOptions, DefaultErrorHandler} = require('assert-options');

const assertOptions = createAssert(new DefaultErrorHandler());
``` 

[Error]:https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error
[TypeError]:https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypeError

---
_Source: https://npm.io/package/assert-options · Machine-readable twin of the npm.io package page. Health data is recomputed on every publish._