The define-properties npm package is used to define new properties on an object, including any necessary descriptors. It provides a simple API to define multiple properties at once while ensuring compatibility with older JavaScript engines that may not fully support ES5.

What are define-properties's main functionalities?

Defining multiple properties

This feature allows you to define multiple properties on an object with their descriptors. The 'enumerable' predicate ensures that the property will only be defined if the value is truthy.

{"object": {}, "properties": {"prop1": {"value": 42, "enumerable": true}, "prop2": {"value": 'hello', "enumerable": false}}, "predicates": {"enumerable": function(val) { return !!val; }}}

Defining properties with shared descriptors

This feature allows you to define properties with a shared descriptor. The predicate function can be used to conditionally define properties based on the key or value.

{"object": {}, "propertyNames": ["prop1", "prop2"], "descriptor": {"enumerable": true}, "predicate": function(key, value) { return key === 'prop1' || value > 10; }}

Other packages similar to define-properties

Readme

Source

define-properties

Define multiple non-enumerable properties at once. Uses Object.defineProperty when available; falls back to standard assignment in older engines. Existing properties are not overridden. Accepts a map of property names to a predicate that, when true, force-overrides.

Example

var define = require('define-properties');
var assert = require('assert');

var obj = define({ a: 1, b: 2 }, {
	a: 10,
	b: 20,
	c: 30
});
assert(obj.a === 1);
assert(obj.b === 2);
assert(obj.c === 30);
if (define.supportsDescriptors) {
	assert.deepEqual(Object.keys(obj), ['a', 'b']);
	assert.deepEqual(Object.getOwnPropertyDescriptor(obj, 'c'), {
		configurable: true,
		enumerable: false,
		value: 30,
		writable: false
	});
}

Then, with predicates:

var define = require('define-properties');
var assert = require('assert');

var obj = define({ a: 1, b: 2, c: 3 }, {
	a: 10,
	b: 20,
	c: 30
}, {
	a: function () { return false; },
	b: function () { return true; }
});
assert(obj.a === 1);
assert(obj.b === 20);
assert(obj.c === 3);
if (define.supportsDescriptors) {
	assert.deepEqual(Object.keys(obj), ['a', 'c']);
	assert.deepEqual(Object.getOwnPropertyDescriptor(obj, 'b'), {
		configurable: true,
		enumerable: false,
		value: 20,
		writable: false
	});
}

Tests

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

Keywords

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Last updated on 15 Apr 2022

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