index.js

'use strict';

var keys = require('object-keys');
var hasSymbols = typeof Symbol === 'function' && typeof Symbol('foo') === 'symbol';

var toStr = Object.prototype.toString;
var concat = Array.prototype.concat;
var origDefineProperty = Object.defineProperty;

var isFunction = function (fn) {
	return typeof fn === 'function' && toStr.call(fn) === '[object Function]';
};

var hasPropertyDescriptors = require('has-property-descriptors')();

var supportsDescriptors = origDefineProperty && hasPropertyDescriptors;

var defineProperty = function (object, name, value, predicate) {
	if (name in object) {
		if (predicate === true) {
			if (object[name] === value) {
				return;
			}
		} else if (!isFunction(predicate) || !predicate()) {
			return;
		}
	}
	if (supportsDescriptors) {
		origDefineProperty(object, name, {
			configurable: true,
			enumerable: false,
			value: value,
			writable: true
		});
	} else {
		object[name] = value; // eslint-disable-line no-param-reassign
	}
};

var defineProperties = function (object, map) {
	var predicates = arguments.length > 2 ? arguments[2] : {};
	var props = keys(map);
	if (hasSymbols) {
		props = concat.call(props, Object.getOwnPropertySymbols(map));
	}
	for (var i = 0; i < props.length; i += 1) {
		defineProperty(object, props[i], map[props[i]], predicates[props[i]]);
	}
};

defineProperties.supportsDescriptors = !!supportsDescriptors;

module.exports = defineProperties;