_define: Return an object with a property defined in a class prototype manner

_define.js

// 209/154 byte/gzip

/**
* Return an object with a property defined in a class prototype manner
* @param {T} object object on which to define the property
* @param {String|Symbol} key name or symbol to be defined
* @param {Descriptor} proto descriptor for the property being defined
* @template T
* @return {T}
*/
function _define(object, key, proto) {
	var descriptor = { configurable: 'configurable' in proto ? proto.configurable : true };

	if ('value' in proto) {
		descriptor.value = proto;
		descriptor.writable = 'writable' in proto ? proto.writable : true;
	} else {
		descriptor.get = proto.get;
		descriptor.set = proto.set;
	}

	return Object.defineProperty(object, key, descriptor);
}

/**
* @typedef {Object} Descriptor
* @property {boolean} [configurable] whether the property may be changed or deleted
* @property {boolean} [enumerable] whether the property may be enumerated
* @property {function} [get] getter for the property which returns the computed value
* @property {function} [set] setter for the property
* @property {any} [value] value associated with the property
* @property {boolean} [writable] whether the property may be assigned
*/

_define.sugar.js

// 227/163 byte/gzip

/**
* Return an object with a property defined in a class prototype manner
* @param {T} object object on which to define the property
* @param {String|Symbol} key name or symbol to be defined
* @param {Descriptor} proto descriptor for the property being defined
* @template T
* @return {T}
*/
function _define(object, key, proto) {
	var descriptor = { configurable: 'configurable' in proto ? proto.configurable : true };

	if ('get' in proto || 'set' in proto) {
		descriptor.get = proto.get;
		descriptor.set = proto.set;
	} else {
		descriptor.value = proto.value || proto;
		descriptor.writable = 'writable' in proto ? proto.writable : true;
	}

	return Object.defineProperty(object, key, descriptor);
}

/**
* @typedef {Object} Descriptor
* @property {boolean} [configurable] whether the property may be changed or deleted
* @property {boolean} [enumerable] whether the property may be enumerated
* @property {function} [get] getter for the property which returns the computed value
* @property {function} [set] setter for the property
* @property {any} [value] value associated with the property
* @property {boolean} [writable] whether the property may be assigned
*/

usage.js

// _define.js:

test = _define(
	_define(
		{},
		'foo', { value: function () { return true } }
	),
	'bar', { get: function () { return true } }
);

console.log({
	isFooConfigurable:  Object.getOwnPropertyDescriptor(test, 'foo').configurable === true,
	isFooWritable:      Object.getOwnPropertyDescriptor(test, 'foo').writable === true,
	isFooNotEnumerable: Object.getOwnPropertyDescriptor(test, 'foo').enumerable === false,
	isFooInvokedTrue:   test.foo(),
	isBarConfigurable:  Object.getOwnPropertyDescriptor(test, 'bar').configurable === true,
	isBarSansWritable:  'writable' in Object.getOwnPropertyDescriptor(test, 'bar') === false,
	isBarNotEnumerable: Object.getOwnPropertyDescriptor(test, 'bar').enumerable === false,
	isBarFalse:         test.bar
});

// _define.sugar.js:

test = _define(
	_define(
		{},
		'foo', function () { return true }
	),
	'bar', { get: function () { return true } }
);

console.log({
	isFooConfigurable:  Object.getOwnPropertyDescriptor(test, 'foo').configurable === true,
	isFooWritable:      Object.getOwnPropertyDescriptor(test, 'foo').writable === true,
	isFooNotEnumerable: Object.getOwnPropertyDescriptor(test, 'foo').enumerable === false,
	isFooInvokedTrue:   test.foo(),
	isBarConfigurable:  Object.getOwnPropertyDescriptor(test, 'bar').configurable === true,
	isBarSansWritable:  'writable' in Object.getOwnPropertyDescriptor(test, 'bar') === false,
	isBarNotEnumerable: Object.getOwnPropertyDescriptor(test, 'bar').enumerable === false,
	isBarFalse:         test.bar
});