is-descriptor

What is is-descriptor?

The is-descriptor npm package is used for checking if an object is a valid descriptor. Descriptors are objects that define the behavior of properties on JavaScript objects, such as whether they are writable, enumerable, or configurable, and they can also specify getter and setter functions. This package is useful for validation in libraries that manipulate object properties and descriptors, ensuring that operations like defining new properties or modifying existing ones are performed with valid descriptor objects.

What are is-descriptor's main functionalities?

Checking property descriptors

This feature allows you to check if a given object is a valid property descriptor. The code sample demonstrates checking various objects to see if they qualify as descriptors based on their properties.

const isDescriptor = require('is-descriptor');

console.log(isDescriptor({enumerable: false, configurable: true})); // true
console.log(isDescriptor({value: 'hello'})); // true
console.log(isDescriptor({get: function() {}})); // true
console.log(isDescriptor({set: undefined})); // false

Other packages similar to is-descriptor

is-data-descriptor

This package checks specifically for data descriptors, which are a type of property descriptor focusing on value properties rather than accessor properties (getters and setters). It's more specific compared to is-descriptor, which checks for both data and accessor descriptors.

is-accessor-descriptor

Similar to is-data-descriptor, this package focuses on checking for accessor descriptors, which define getter and setter functions for a property. It complements is-data-descriptor by covering the other main type of property descriptor, offering a more focused approach compared to the broader checks performed by is-descriptor.

README

is-descriptor

Returns true if a value has the characteristics of a valid JavaScript descriptor. Works for data descriptors and accessor descriptors.

Usage

const isDescriptor = require('is-descriptor');
const assert = require('assert');

assert.equal(isDescriptor({ value: 'foo' }), true);
assert.equal(isDescriptor({ get() {}, set() {} }), true);
assert.equal(isDescriptor({ get: 'foo', set() {} }), false);

You may also check for a descriptor by passing an object as the first argument and property name (string) as the second argument.

const obj = { foo: 'abc' };

Object.defineProperty(obj, 'bar', {
  value: 'xyz'
});

assert.equal(isDescriptor(obj, 'foo'), true);
assert.equal(isDescriptor(obj, 'bar'), true);

Examples

value type

false when not an object

assert.equal(isDescriptor('a'), false);
assert.equal(isDescriptor(null), false);
assert.equal(isDescriptor([]), false);

data descriptor

true when the object has valid properties with valid values.

assert.equal(isDescriptor({ value: 'foo' }), true);
assert.equal(isDescriptor({ value() {} }), true);

false when the object has invalid properties

assert.equal(isDescriptor({ value: 'foo', enumerable: 'baz' }), false);
assert.equal(isDescriptor({ value: 'foo', configurable: 'baz' }), false);
assert.equal(isDescriptor({ value: 'foo', get() {} }), false);
assert.equal(isDescriptor({ get() {}, value() {} }), false);

false when a value is not the correct type

assert.equal(isDescriptor({ value: 'foo', enumerable: 'foo' }), false);
assert.equal(isDescriptor({ value: 'foo', configurable: 'foo' }), false);
assert.equal(isDescriptor({ value: 'foo', writable: 'foo' }), false);

accessor descriptor

true when the object has valid properties with valid values.

assert.equal(isDescriptor({ get() {}, set() {} }), true);
assert.equal(isDescriptor({ get() {} }), true);
assert.equal(isDescriptor({ set() {} }), true);

false when the object has invalid properties

assert.equal(isDescriptor({ get() {}, set() {}, enumerable: 'baz' }), false);
assert.equal(isDescriptor({ get() {}, writable: true }), false);
assert.equal(isDescriptor({ get() {}, value: true }), false);

false when an accessor is not a function

assert.equal(isDescriptor({ get() {}, set: 'baz' }), false);
assert.equal(isDescriptor({ get: 'foo', set() {} }), false);
assert.equal(isDescriptor({ get: 'foo', bar: 'baz' }), false);
assert.equal(isDescriptor({ get: 'foo', set: 'baz' }), false);

false when a value is not the correct type

assert.equal(isDescriptor({ get() {}, set() {}, enumerable: 'foo' }), false);
assert.equal(isDescriptor({ set() {}, configurable: 'foo' }), false);
assert.equal(isDescriptor({ get() {}, configurable: 'foo' }), false);

Related projects

You might also be interested in these projects:

• is-accessor-descriptor: Returns true if a value has the characteristics of a valid JavaScript accessor descriptor.
• is-data-descriptor: Returns true if a value has the characteristics of a valid JavaScript data descriptor.
• is-object: Returns true if the value is an object and not an array or null.

Tests

Simply clone the repo, npm install, and run npm test

Changelog

v1.0.3 - 2023-10-26

Commits

• [eslint] actually use eslint 8bcf028
• [meta] update package.json, gitignore from main 544cdfe
• [readme] update readme from main 1130f79
• [Tests] switch to tape 3f8f094
• [Docs] remove verb 92ee1bf
• [Tests] migrate from travis to github actions 8da3a3c
• [Fix] a descriptor with set and not get is still an accessor descriptor 269fb53
• [patch] switch from files to exports 41b2d61
• [Fix] allow any non-primitive; arrays and functions are objects too 9fd1ac8
• [Deps] update is-accessor-descriptor, is-data-descriptor f4dbc73
• [Tests] make a test dir 9eaa17c