assert-options
v0.8.2
Published
Generic options parameter handling.
Downloads
1,291,867
Readme
assert-options
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
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:
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:
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
isnull
/undefined
, new{}
is returned, applyingdefaults
as specified.When
options
contains an unknown property, ErrorOption "name" is not recognized.
is thrown.When a property in
options
is missing orundefined
, its value is set from thedefaults
, provided it is available and its value is notundefined
.When
options
is notnull
/undefined
, it must be of typeobject
, 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:
const {createOptions, DefaultErrorHandler} = require('assert-options');
const assertOptions = createAssert(new DefaultErrorHandler());