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is-descriptor

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is-descriptor

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


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2
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35,947,877
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Package description

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

Readme

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

Usage

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

const defaults = { configurable: false, enumerable: false };
const dataDefaults = { ...defaults, writable: false};

assert.ok(isDescriptor({ ...dataDefaults, value: 'foo' }));
assert.ok(isDescriptor({ ...defaults, get() {}, set() {} }));
assert.ok(!isDescriptor({ ...defaults, get: 'foo', set() {} }));

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' });
Reflect.defineProperty(obj, 'baz', { value: 'xyz' });

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

Examples

value type

Returns false when not an object

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

data descriptor

Returns true when the object has valid properties with valid values.

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

Returns false when the object has invalid properties

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

false when a value is not the correct type

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

accessor descriptor

true when the object has valid properties with valid values.

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

false when the object has invalid properties

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

Returns false when an accessor is not a function

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

Returns false when a value is not the correct type

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

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

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Last updated on 28 Oct 2023

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